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1/*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright IBM Corporation, 2008
19 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
23 *
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 *
27 * For detailed explanation of Read-Copy Update mechanism see -
28 * Documentation/RCU
29 */
30#include <linux/types.h>
31#include <linux/kernel.h>
32#include <linux/init.h>
33#include <linux/spinlock.h>
34#include <linux/smp.h>
35#include <linux/rcupdate.h>
36#include <linux/interrupt.h>
37#include <linux/sched.h>
38#include <linux/nmi.h>
39#include <linux/atomic.h>
40#include <linux/bitops.h>
41#include <linux/export.h>
42#include <linux/completion.h>
43#include <linux/moduleparam.h>
44#include <linux/module.h>
45#include <linux/percpu.h>
46#include <linux/notifier.h>
47#include <linux/cpu.h>
48#include <linux/mutex.h>
49#include <linux/time.h>
50#include <linux/kernel_stat.h>
51#include <linux/wait.h>
52#include <linux/kthread.h>
53#include <linux/prefetch.h>
54#include <linux/delay.h>
55#include <linux/stop_machine.h>
56#include <linux/random.h>
57#include <linux/trace_events.h>
58#include <linux/suspend.h>
59
60#include "tree.h"
61#include "rcu.h"
62
63MODULE_ALIAS("rcutree");
64#ifdef MODULE_PARAM_PREFIX
65#undef MODULE_PARAM_PREFIX
66#endif
67#define MODULE_PARAM_PREFIX "rcutree."
68
69/* Data structures. */
70
71/*
72 * In order to export the rcu_state name to the tracing tools, it
73 * needs to be added in the __tracepoint_string section.
74 * This requires defining a separate variable tp_<sname>_varname
75 * that points to the string being used, and this will allow
76 * the tracing userspace tools to be able to decipher the string
77 * address to the matching string.
78 */
79#ifdef CONFIG_TRACING
80# define DEFINE_RCU_TPS(sname) \
81static char sname##_varname[] = #sname; \
82static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
83# define RCU_STATE_NAME(sname) sname##_varname
84#else
85# define DEFINE_RCU_TPS(sname)
86# define RCU_STATE_NAME(sname) __stringify(sname)
87#endif
88
89#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
90DEFINE_RCU_TPS(sname) \
91static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
92struct rcu_state sname##_state = { \
93 .level = { &sname##_state.node[0] }, \
94 .rda = &sname##_data, \
95 .call = cr, \
96 .gp_state = RCU_GP_IDLE, \
97 .gpnum = 0UL - 300UL, \
98 .completed = 0UL - 300UL, \
99 .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
100 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
101 .orphan_donetail = &sname##_state.orphan_donelist, \
102 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
103 .name = RCU_STATE_NAME(sname), \
104 .abbr = sabbr, \
105}
106
107RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
108RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
109
110static struct rcu_state *const rcu_state_p;
111LIST_HEAD(rcu_struct_flavors);
112
113/* Dump rcu_node combining tree at boot to verify correct setup. */
114static bool dump_tree;
115module_param(dump_tree, bool, 0444);
116/* Control rcu_node-tree auto-balancing at boot time. */
117static bool rcu_fanout_exact;
118module_param(rcu_fanout_exact, bool, 0444);
119/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
120static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
121module_param(rcu_fanout_leaf, int, 0444);
122int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
123/* Number of rcu_nodes at specified level. */
124static int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
125int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
126
127/*
128 * The rcu_scheduler_active variable transitions from zero to one just
129 * before the first task is spawned. So when this variable is zero, RCU
130 * can assume that there is but one task, allowing RCU to (for example)
131 * optimize synchronize_sched() to a simple barrier(). When this variable
132 * is one, RCU must actually do all the hard work required to detect real
133 * grace periods. This variable is also used to suppress boot-time false
134 * positives from lockdep-RCU error checking.
135 */
136int rcu_scheduler_active __read_mostly;
137EXPORT_SYMBOL_GPL(rcu_scheduler_active);
138
139/*
140 * The rcu_scheduler_fully_active variable transitions from zero to one
141 * during the early_initcall() processing, which is after the scheduler
142 * is capable of creating new tasks. So RCU processing (for example,
143 * creating tasks for RCU priority boosting) must be delayed until after
144 * rcu_scheduler_fully_active transitions from zero to one. We also
145 * currently delay invocation of any RCU callbacks until after this point.
146 *
147 * It might later prove better for people registering RCU callbacks during
148 * early boot to take responsibility for these callbacks, but one step at
149 * a time.
150 */
151static int rcu_scheduler_fully_active __read_mostly;
152
153static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
154static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
155static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
156static void invoke_rcu_core(void);
157static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
158static void rcu_report_exp_rdp(struct rcu_state *rsp,
159 struct rcu_data *rdp, bool wake);
160
161/* rcuc/rcub kthread realtime priority */
162#ifdef CONFIG_RCU_KTHREAD_PRIO
163static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
164#else /* #ifdef CONFIG_RCU_KTHREAD_PRIO */
165static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
166#endif /* #else #ifdef CONFIG_RCU_KTHREAD_PRIO */
167module_param(kthread_prio, int, 0644);
168
169/* Delay in jiffies for grace-period initialization delays, debug only. */
170
171#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT
172static int gp_preinit_delay = CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT_DELAY;
173module_param(gp_preinit_delay, int, 0644);
174#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
175static const int gp_preinit_delay;
176#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
177
178#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT
179static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY;
180module_param(gp_init_delay, int, 0644);
181#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
182static const int gp_init_delay;
183#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
184
185#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP
186static int gp_cleanup_delay = CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY;
187module_param(gp_cleanup_delay, int, 0644);
188#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
189static const int gp_cleanup_delay;
190#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
191
192/*
193 * Number of grace periods between delays, normalized by the duration of
194 * the delay. The longer the the delay, the more the grace periods between
195 * each delay. The reason for this normalization is that it means that,
196 * for non-zero delays, the overall slowdown of grace periods is constant
197 * regardless of the duration of the delay. This arrangement balances
198 * the need for long delays to increase some race probabilities with the
199 * need for fast grace periods to increase other race probabilities.
200 */
201#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
202
203/*
204 * Track the rcutorture test sequence number and the update version
205 * number within a given test. The rcutorture_testseq is incremented
206 * on every rcutorture module load and unload, so has an odd value
207 * when a test is running. The rcutorture_vernum is set to zero
208 * when rcutorture starts and is incremented on each rcutorture update.
209 * These variables enable correlating rcutorture output with the
210 * RCU tracing information.
211 */
212unsigned long rcutorture_testseq;
213unsigned long rcutorture_vernum;
214
215/*
216 * Compute the mask of online CPUs for the specified rcu_node structure.
217 * This will not be stable unless the rcu_node structure's ->lock is
218 * held, but the bit corresponding to the current CPU will be stable
219 * in most contexts.
220 */
221unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
222{
223 return READ_ONCE(rnp->qsmaskinitnext);
224}
225
226/*
227 * Return true if an RCU grace period is in progress. The READ_ONCE()s
228 * permit this function to be invoked without holding the root rcu_node
229 * structure's ->lock, but of course results can be subject to change.
230 */
231static int rcu_gp_in_progress(struct rcu_state *rsp)
232{
233 return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum);
234}
235
236/*
237 * Note a quiescent state. Because we do not need to know
238 * how many quiescent states passed, just if there was at least
239 * one since the start of the grace period, this just sets a flag.
240 * The caller must have disabled preemption.
241 */
242void rcu_sched_qs(void)
243{
244 if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
245 return;
246 trace_rcu_grace_period(TPS("rcu_sched"),
247 __this_cpu_read(rcu_sched_data.gpnum),
248 TPS("cpuqs"));
249 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
250 if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
251 return;
252 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
253 rcu_report_exp_rdp(&rcu_sched_state,
254 this_cpu_ptr(&rcu_sched_data), true);
255}
256
257void rcu_bh_qs(void)
258{
259 if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
260 trace_rcu_grace_period(TPS("rcu_bh"),
261 __this_cpu_read(rcu_bh_data.gpnum),
262 TPS("cpuqs"));
263 __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
264 }
265}
266
267static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
268
269static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
270 .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
271 .dynticks = ATOMIC_INIT(1),
272#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
273 .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
274 .dynticks_idle = ATOMIC_INIT(1),
275#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
276};
277
278DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
279EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
280
281/*
282 * Let the RCU core know that this CPU has gone through the scheduler,
283 * which is a quiescent state. This is called when the need for a
284 * quiescent state is urgent, so we burn an atomic operation and full
285 * memory barriers to let the RCU core know about it, regardless of what
286 * this CPU might (or might not) do in the near future.
287 *
288 * We inform the RCU core by emulating a zero-duration dyntick-idle
289 * period, which we in turn do by incrementing the ->dynticks counter
290 * by two.
291 *
292 * The caller must have disabled interrupts.
293 */
294static void rcu_momentary_dyntick_idle(void)
295{
296 struct rcu_data *rdp;
297 struct rcu_dynticks *rdtp;
298 int resched_mask;
299 struct rcu_state *rsp;
300
301 /*
302 * Yes, we can lose flag-setting operations. This is OK, because
303 * the flag will be set again after some delay.
304 */
305 resched_mask = raw_cpu_read(rcu_sched_qs_mask);
306 raw_cpu_write(rcu_sched_qs_mask, 0);
307
308 /* Find the flavor that needs a quiescent state. */
309 for_each_rcu_flavor(rsp) {
310 rdp = raw_cpu_ptr(rsp->rda);
311 if (!(resched_mask & rsp->flavor_mask))
312 continue;
313 smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */
314 if (READ_ONCE(rdp->mynode->completed) !=
315 READ_ONCE(rdp->cond_resched_completed))
316 continue;
317
318 /*
319 * Pretend to be momentarily idle for the quiescent state.
320 * This allows the grace-period kthread to record the
321 * quiescent state, with no need for this CPU to do anything
322 * further.
323 */
324 rdtp = this_cpu_ptr(&rcu_dynticks);
325 smp_mb__before_atomic(); /* Earlier stuff before QS. */
326 atomic_add(2, &rdtp->dynticks); /* QS. */
327 smp_mb__after_atomic(); /* Later stuff after QS. */
328 break;
329 }
330}
331
332/*
333 * Note a context switch. This is a quiescent state for RCU-sched,
334 * and requires special handling for preemptible RCU.
335 * The caller must have disabled interrupts.
336 */
337void rcu_note_context_switch(void)
338{
339 barrier(); /* Avoid RCU read-side critical sections leaking down. */
340 trace_rcu_utilization(TPS("Start context switch"));
341 rcu_sched_qs();
342 rcu_preempt_note_context_switch();
343 if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
344 rcu_momentary_dyntick_idle();
345 trace_rcu_utilization(TPS("End context switch"));
346 barrier(); /* Avoid RCU read-side critical sections leaking up. */
347}
348EXPORT_SYMBOL_GPL(rcu_note_context_switch);
349
350/*
351 * Register a quiescent state for all RCU flavors. If there is an
352 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
353 * dyntick-idle quiescent state visible to other CPUs (but only for those
354 * RCU flavors in desperate need of a quiescent state, which will normally
355 * be none of them). Either way, do a lightweight quiescent state for
356 * all RCU flavors.
357 *
358 * The barrier() calls are redundant in the common case when this is
359 * called externally, but just in case this is called from within this
360 * file.
361 *
362 */
363void rcu_all_qs(void)
364{
365 unsigned long flags;
366
367 barrier(); /* Avoid RCU read-side critical sections leaking down. */
368 if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) {
369 local_irq_save(flags);
370 rcu_momentary_dyntick_idle();
371 local_irq_restore(flags);
372 }
373 this_cpu_inc(rcu_qs_ctr);
374 barrier(); /* Avoid RCU read-side critical sections leaking up. */
375}
376EXPORT_SYMBOL_GPL(rcu_all_qs);
377
378static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */
379static long qhimark = 10000; /* If this many pending, ignore blimit. */
380static long qlowmark = 100; /* Once only this many pending, use blimit. */
381
382module_param(blimit, long, 0444);
383module_param(qhimark, long, 0444);
384module_param(qlowmark, long, 0444);
385
386static ulong jiffies_till_first_fqs = ULONG_MAX;
387static ulong jiffies_till_next_fqs = ULONG_MAX;
388
389module_param(jiffies_till_first_fqs, ulong, 0644);
390module_param(jiffies_till_next_fqs, ulong, 0644);
391
392/*
393 * How long the grace period must be before we start recruiting
394 * quiescent-state help from rcu_note_context_switch().
395 */
396static ulong jiffies_till_sched_qs = HZ / 20;
397module_param(jiffies_till_sched_qs, ulong, 0644);
398
399static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
400 struct rcu_data *rdp);
401static void force_qs_rnp(struct rcu_state *rsp,
402 int (*f)(struct rcu_data *rsp, bool *isidle,
403 unsigned long *maxj),
404 bool *isidle, unsigned long *maxj);
405static void force_quiescent_state(struct rcu_state *rsp);
406static int rcu_pending(void);
407
408/*
409 * Return the number of RCU batches started thus far for debug & stats.
410 */
411unsigned long rcu_batches_started(void)
412{
413 return rcu_state_p->gpnum;
414}
415EXPORT_SYMBOL_GPL(rcu_batches_started);
416
417/*
418 * Return the number of RCU-sched batches started thus far for debug & stats.
419 */
420unsigned long rcu_batches_started_sched(void)
421{
422 return rcu_sched_state.gpnum;
423}
424EXPORT_SYMBOL_GPL(rcu_batches_started_sched);
425
426/*
427 * Return the number of RCU BH batches started thus far for debug & stats.
428 */
429unsigned long rcu_batches_started_bh(void)
430{
431 return rcu_bh_state.gpnum;
432}
433EXPORT_SYMBOL_GPL(rcu_batches_started_bh);
434
435/*
436 * Return the number of RCU batches completed thus far for debug & stats.
437 */
438unsigned long rcu_batches_completed(void)
439{
440 return rcu_state_p->completed;
441}
442EXPORT_SYMBOL_GPL(rcu_batches_completed);
443
444/*
445 * Return the number of RCU-sched batches completed thus far for debug & stats.
446 */
447unsigned long rcu_batches_completed_sched(void)
448{
449 return rcu_sched_state.completed;
450}
451EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
452
453/*
454 * Return the number of RCU BH batches completed thus far for debug & stats.
455 */
456unsigned long rcu_batches_completed_bh(void)
457{
458 return rcu_bh_state.completed;
459}
460EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
461
462/*
463 * Force a quiescent state.
464 */
465void rcu_force_quiescent_state(void)
466{
467 force_quiescent_state(rcu_state_p);
468}
469EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
470
471/*
472 * Force a quiescent state for RCU BH.
473 */
474void rcu_bh_force_quiescent_state(void)
475{
476 force_quiescent_state(&rcu_bh_state);
477}
478EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
479
480/*
481 * Force a quiescent state for RCU-sched.
482 */
483void rcu_sched_force_quiescent_state(void)
484{
485 force_quiescent_state(&rcu_sched_state);
486}
487EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
488
489/*
490 * Show the state of the grace-period kthreads.
491 */
492void show_rcu_gp_kthreads(void)
493{
494 struct rcu_state *rsp;
495
496 for_each_rcu_flavor(rsp) {
497 pr_info("%s: wait state: %d ->state: %#lx\n",
498 rsp->name, rsp->gp_state, rsp->gp_kthread->state);
499 /* sched_show_task(rsp->gp_kthread); */
500 }
501}
502EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
503
504/*
505 * Record the number of times rcutorture tests have been initiated and
506 * terminated. This information allows the debugfs tracing stats to be
507 * correlated to the rcutorture messages, even when the rcutorture module
508 * is being repeatedly loaded and unloaded. In other words, we cannot
509 * store this state in rcutorture itself.
510 */
511void rcutorture_record_test_transition(void)
512{
513 rcutorture_testseq++;
514 rcutorture_vernum = 0;
515}
516EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
517
518/*
519 * Send along grace-period-related data for rcutorture diagnostics.
520 */
521void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
522 unsigned long *gpnum, unsigned long *completed)
523{
524 struct rcu_state *rsp = NULL;
525
526 switch (test_type) {
527 case RCU_FLAVOR:
528 rsp = rcu_state_p;
529 break;
530 case RCU_BH_FLAVOR:
531 rsp = &rcu_bh_state;
532 break;
533 case RCU_SCHED_FLAVOR:
534 rsp = &rcu_sched_state;
535 break;
536 default:
537 break;
538 }
539 if (rsp != NULL) {
540 *flags = READ_ONCE(rsp->gp_flags);
541 *gpnum = READ_ONCE(rsp->gpnum);
542 *completed = READ_ONCE(rsp->completed);
543 return;
544 }
545 *flags = 0;
546 *gpnum = 0;
547 *completed = 0;
548}
549EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
550
551/*
552 * Record the number of writer passes through the current rcutorture test.
553 * This is also used to correlate debugfs tracing stats with the rcutorture
554 * messages.
555 */
556void rcutorture_record_progress(unsigned long vernum)
557{
558 rcutorture_vernum++;
559}
560EXPORT_SYMBOL_GPL(rcutorture_record_progress);
561
562/*
563 * Does the CPU have callbacks ready to be invoked?
564 */
565static int
566cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
567{
568 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
569 rdp->nxttail[RCU_DONE_TAIL] != NULL;
570}
571
572/*
573 * Return the root node of the specified rcu_state structure.
574 */
575static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
576{
577 return &rsp->node[0];
578}
579
580/*
581 * Is there any need for future grace periods?
582 * Interrupts must be disabled. If the caller does not hold the root
583 * rnp_node structure's ->lock, the results are advisory only.
584 */
585static int rcu_future_needs_gp(struct rcu_state *rsp)
586{
587 struct rcu_node *rnp = rcu_get_root(rsp);
588 int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
589 int *fp = &rnp->need_future_gp[idx];
590
591 return READ_ONCE(*fp);
592}
593
594/*
595 * Does the current CPU require a not-yet-started grace period?
596 * The caller must have disabled interrupts to prevent races with
597 * normal callback registry.
598 */
599static bool
600cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
601{
602 int i;
603
604 if (rcu_gp_in_progress(rsp))
605 return false; /* No, a grace period is already in progress. */
606 if (rcu_future_needs_gp(rsp))
607 return true; /* Yes, a no-CBs CPU needs one. */
608 if (!rdp->nxttail[RCU_NEXT_TAIL])
609 return false; /* No, this is a no-CBs (or offline) CPU. */
610 if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
611 return true; /* Yes, CPU has newly registered callbacks. */
612 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
613 if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
614 ULONG_CMP_LT(READ_ONCE(rsp->completed),
615 rdp->nxtcompleted[i]))
616 return true; /* Yes, CBs for future grace period. */
617 return false; /* No grace period needed. */
618}
619
620/*
621 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
622 *
623 * If the new value of the ->dynticks_nesting counter now is zero,
624 * we really have entered idle, and must do the appropriate accounting.
625 * The caller must have disabled interrupts.
626 */
627static void rcu_eqs_enter_common(long long oldval, bool user)
628{
629 struct rcu_state *rsp;
630 struct rcu_data *rdp;
631 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
632
633 trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
634 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
635 !user && !is_idle_task(current)) {
636 struct task_struct *idle __maybe_unused =
637 idle_task(smp_processor_id());
638
639 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
640 ftrace_dump(DUMP_ORIG);
641 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
642 current->pid, current->comm,
643 idle->pid, idle->comm); /* must be idle task! */
644 }
645 for_each_rcu_flavor(rsp) {
646 rdp = this_cpu_ptr(rsp->rda);
647 do_nocb_deferred_wakeup(rdp);
648 }
649 rcu_prepare_for_idle();
650 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
651 smp_mb__before_atomic(); /* See above. */
652 atomic_inc(&rdtp->dynticks);
653 smp_mb__after_atomic(); /* Force ordering with next sojourn. */
654 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
655 atomic_read(&rdtp->dynticks) & 0x1);
656 rcu_dynticks_task_enter();
657
658 /*
659 * It is illegal to enter an extended quiescent state while
660 * in an RCU read-side critical section.
661 */
662 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
663 "Illegal idle entry in RCU read-side critical section.");
664 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),
665 "Illegal idle entry in RCU-bh read-side critical section.");
666 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),
667 "Illegal idle entry in RCU-sched read-side critical section.");
668}
669
670/*
671 * Enter an RCU extended quiescent state, which can be either the
672 * idle loop or adaptive-tickless usermode execution.
673 */
674static void rcu_eqs_enter(bool user)
675{
676 long long oldval;
677 struct rcu_dynticks *rdtp;
678
679 rdtp = this_cpu_ptr(&rcu_dynticks);
680 oldval = rdtp->dynticks_nesting;
681 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
682 (oldval & DYNTICK_TASK_NEST_MASK) == 0);
683 if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
684 rdtp->dynticks_nesting = 0;
685 rcu_eqs_enter_common(oldval, user);
686 } else {
687 rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
688 }
689}
690
691/**
692 * rcu_idle_enter - inform RCU that current CPU is entering idle
693 *
694 * Enter idle mode, in other words, -leave- the mode in which RCU
695 * read-side critical sections can occur. (Though RCU read-side
696 * critical sections can occur in irq handlers in idle, a possibility
697 * handled by irq_enter() and irq_exit().)
698 *
699 * We crowbar the ->dynticks_nesting field to zero to allow for
700 * the possibility of usermode upcalls having messed up our count
701 * of interrupt nesting level during the prior busy period.
702 */
703void rcu_idle_enter(void)
704{
705 unsigned long flags;
706
707 local_irq_save(flags);
708 rcu_eqs_enter(false);
709 rcu_sysidle_enter(0);
710 local_irq_restore(flags);
711}
712EXPORT_SYMBOL_GPL(rcu_idle_enter);
713
714#ifdef CONFIG_NO_HZ_FULL
715/**
716 * rcu_user_enter - inform RCU that we are resuming userspace.
717 *
718 * Enter RCU idle mode right before resuming userspace. No use of RCU
719 * is permitted between this call and rcu_user_exit(). This way the
720 * CPU doesn't need to maintain the tick for RCU maintenance purposes
721 * when the CPU runs in userspace.
722 */
723void rcu_user_enter(void)
724{
725 rcu_eqs_enter(1);
726}
727#endif /* CONFIG_NO_HZ_FULL */
728
729/**
730 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
731 *
732 * Exit from an interrupt handler, which might possibly result in entering
733 * idle mode, in other words, leaving the mode in which read-side critical
734 * sections can occur. The caller must have disabled interrupts.
735 *
736 * This code assumes that the idle loop never does anything that might
737 * result in unbalanced calls to irq_enter() and irq_exit(). If your
738 * architecture violates this assumption, RCU will give you what you
739 * deserve, good and hard. But very infrequently and irreproducibly.
740 *
741 * Use things like work queues to work around this limitation.
742 *
743 * You have been warned.
744 */
745void rcu_irq_exit(void)
746{
747 long long oldval;
748 struct rcu_dynticks *rdtp;
749
750 RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!");
751 rdtp = this_cpu_ptr(&rcu_dynticks);
752 oldval = rdtp->dynticks_nesting;
753 rdtp->dynticks_nesting--;
754 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
755 rdtp->dynticks_nesting < 0);
756 if (rdtp->dynticks_nesting)
757 trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
758 else
759 rcu_eqs_enter_common(oldval, true);
760 rcu_sysidle_enter(1);
761}
762
763/*
764 * Wrapper for rcu_irq_exit() where interrupts are enabled.
765 */
766void rcu_irq_exit_irqson(void)
767{
768 unsigned long flags;
769
770 local_irq_save(flags);
771 rcu_irq_exit();
772 local_irq_restore(flags);
773}
774
775/*
776 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
777 *
778 * If the new value of the ->dynticks_nesting counter was previously zero,
779 * we really have exited idle, and must do the appropriate accounting.
780 * The caller must have disabled interrupts.
781 */
782static void rcu_eqs_exit_common(long long oldval, int user)
783{
784 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
785
786 rcu_dynticks_task_exit();
787 smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */
788 atomic_inc(&rdtp->dynticks);
789 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
790 smp_mb__after_atomic(); /* See above. */
791 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
792 !(atomic_read(&rdtp->dynticks) & 0x1));
793 rcu_cleanup_after_idle();
794 trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
795 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
796 !user && !is_idle_task(current)) {
797 struct task_struct *idle __maybe_unused =
798 idle_task(smp_processor_id());
799
800 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
801 oldval, rdtp->dynticks_nesting);
802 ftrace_dump(DUMP_ORIG);
803 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
804 current->pid, current->comm,
805 idle->pid, idle->comm); /* must be idle task! */
806 }
807}
808
809/*
810 * Exit an RCU extended quiescent state, which can be either the
811 * idle loop or adaptive-tickless usermode execution.
812 */
813static void rcu_eqs_exit(bool user)
814{
815 struct rcu_dynticks *rdtp;
816 long long oldval;
817
818 rdtp = this_cpu_ptr(&rcu_dynticks);
819 oldval = rdtp->dynticks_nesting;
820 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
821 if (oldval & DYNTICK_TASK_NEST_MASK) {
822 rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
823 } else {
824 rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
825 rcu_eqs_exit_common(oldval, user);
826 }
827}
828
829/**
830 * rcu_idle_exit - inform RCU that current CPU is leaving idle
831 *
832 * Exit idle mode, in other words, -enter- the mode in which RCU
833 * read-side critical sections can occur.
834 *
835 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
836 * allow for the possibility of usermode upcalls messing up our count
837 * of interrupt nesting level during the busy period that is just
838 * now starting.
839 */
840void rcu_idle_exit(void)
841{
842 unsigned long flags;
843
844 local_irq_save(flags);
845 rcu_eqs_exit(false);
846 rcu_sysidle_exit(0);
847 local_irq_restore(flags);
848}
849EXPORT_SYMBOL_GPL(rcu_idle_exit);
850
851#ifdef CONFIG_NO_HZ_FULL
852/**
853 * rcu_user_exit - inform RCU that we are exiting userspace.
854 *
855 * Exit RCU idle mode while entering the kernel because it can
856 * run a RCU read side critical section anytime.
857 */
858void rcu_user_exit(void)
859{
860 rcu_eqs_exit(1);
861}
862#endif /* CONFIG_NO_HZ_FULL */
863
864/**
865 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
866 *
867 * Enter an interrupt handler, which might possibly result in exiting
868 * idle mode, in other words, entering the mode in which read-side critical
869 * sections can occur. The caller must have disabled interrupts.
870 *
871 * Note that the Linux kernel is fully capable of entering an interrupt
872 * handler that it never exits, for example when doing upcalls to
873 * user mode! This code assumes that the idle loop never does upcalls to
874 * user mode. If your architecture does do upcalls from the idle loop (or
875 * does anything else that results in unbalanced calls to the irq_enter()
876 * and irq_exit() functions), RCU will give you what you deserve, good
877 * and hard. But very infrequently and irreproducibly.
878 *
879 * Use things like work queues to work around this limitation.
880 *
881 * You have been warned.
882 */
883void rcu_irq_enter(void)
884{
885 struct rcu_dynticks *rdtp;
886 long long oldval;
887
888 RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!");
889 rdtp = this_cpu_ptr(&rcu_dynticks);
890 oldval = rdtp->dynticks_nesting;
891 rdtp->dynticks_nesting++;
892 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
893 rdtp->dynticks_nesting == 0);
894 if (oldval)
895 trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
896 else
897 rcu_eqs_exit_common(oldval, true);
898 rcu_sysidle_exit(1);
899}
900
901/*
902 * Wrapper for rcu_irq_enter() where interrupts are enabled.
903 */
904void rcu_irq_enter_irqson(void)
905{
906 unsigned long flags;
907
908 local_irq_save(flags);
909 rcu_irq_enter();
910 local_irq_restore(flags);
911}
912
913/**
914 * rcu_nmi_enter - inform RCU of entry to NMI context
915 *
916 * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
917 * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
918 * that the CPU is active. This implementation permits nested NMIs, as
919 * long as the nesting level does not overflow an int. (You will probably
920 * run out of stack space first.)
921 */
922void rcu_nmi_enter(void)
923{
924 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
925 int incby = 2;
926
927 /* Complain about underflow. */
928 WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
929
930 /*
931 * If idle from RCU viewpoint, atomically increment ->dynticks
932 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
933 * Otherwise, increment ->dynticks_nmi_nesting by two. This means
934 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
935 * to be in the outermost NMI handler that interrupted an RCU-idle
936 * period (observation due to Andy Lutomirski).
937 */
938 if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
939 smp_mb__before_atomic(); /* Force delay from prior write. */
940 atomic_inc(&rdtp->dynticks);
941 /* atomic_inc() before later RCU read-side crit sects */
942 smp_mb__after_atomic(); /* See above. */
943 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
944 incby = 1;
945 }
946 rdtp->dynticks_nmi_nesting += incby;
947 barrier();
948}
949
950/**
951 * rcu_nmi_exit - inform RCU of exit from NMI context
952 *
953 * If we are returning from the outermost NMI handler that interrupted an
954 * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
955 * to let the RCU grace-period handling know that the CPU is back to
956 * being RCU-idle.
957 */
958void rcu_nmi_exit(void)
959{
960 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
961
962 /*
963 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
964 * (We are exiting an NMI handler, so RCU better be paying attention
965 * to us!)
966 */
967 WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
968 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
969
970 /*
971 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
972 * leave it in non-RCU-idle state.
973 */
974 if (rdtp->dynticks_nmi_nesting != 1) {
975 rdtp->dynticks_nmi_nesting -= 2;
976 return;
977 }
978
979 /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
980 rdtp->dynticks_nmi_nesting = 0;
981 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
982 smp_mb__before_atomic(); /* See above. */
983 atomic_inc(&rdtp->dynticks);
984 smp_mb__after_atomic(); /* Force delay to next write. */
985 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
986}
987
988/**
989 * __rcu_is_watching - are RCU read-side critical sections safe?
990 *
991 * Return true if RCU is watching the running CPU, which means that
992 * this CPU can safely enter RCU read-side critical sections. Unlike
993 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
994 * least disabled preemption.
995 */
996bool notrace __rcu_is_watching(void)
997{
998 return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
999}
1000
1001/**
1002 * rcu_is_watching - see if RCU thinks that the current CPU is idle
1003 *
1004 * If the current CPU is in its idle loop and is neither in an interrupt
1005 * or NMI handler, return true.
1006 */
1007bool notrace rcu_is_watching(void)
1008{
1009 bool ret;
1010
1011 preempt_disable_notrace();
1012 ret = __rcu_is_watching();
1013 preempt_enable_notrace();
1014 return ret;
1015}
1016EXPORT_SYMBOL_GPL(rcu_is_watching);
1017
1018#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
1019
1020/*
1021 * Is the current CPU online? Disable preemption to avoid false positives
1022 * that could otherwise happen due to the current CPU number being sampled,
1023 * this task being preempted, its old CPU being taken offline, resuming
1024 * on some other CPU, then determining that its old CPU is now offline.
1025 * It is OK to use RCU on an offline processor during initial boot, hence
1026 * the check for rcu_scheduler_fully_active. Note also that it is OK
1027 * for a CPU coming online to use RCU for one jiffy prior to marking itself
1028 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
1029 * offline to continue to use RCU for one jiffy after marking itself
1030 * offline in the cpu_online_mask. This leniency is necessary given the
1031 * non-atomic nature of the online and offline processing, for example,
1032 * the fact that a CPU enters the scheduler after completing the CPU_DYING
1033 * notifiers.
1034 *
1035 * This is also why RCU internally marks CPUs online during the
1036 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
1037 *
1038 * Disable checking if in an NMI handler because we cannot safely report
1039 * errors from NMI handlers anyway.
1040 */
1041bool rcu_lockdep_current_cpu_online(void)
1042{
1043 struct rcu_data *rdp;
1044 struct rcu_node *rnp;
1045 bool ret;
1046
1047 if (in_nmi())
1048 return true;
1049 preempt_disable();
1050 rdp = this_cpu_ptr(&rcu_sched_data);
1051 rnp = rdp->mynode;
1052 ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
1053 !rcu_scheduler_fully_active;
1054 preempt_enable();
1055 return ret;
1056}
1057EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
1058
1059#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
1060
1061/**
1062 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
1063 *
1064 * If the current CPU is idle or running at a first-level (not nested)
1065 * interrupt from idle, return true. The caller must have at least
1066 * disabled preemption.
1067 */
1068static int rcu_is_cpu_rrupt_from_idle(void)
1069{
1070 return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
1071}
1072
1073/*
1074 * Snapshot the specified CPU's dynticks counter so that we can later
1075 * credit them with an implicit quiescent state. Return 1 if this CPU
1076 * is in dynticks idle mode, which is an extended quiescent state.
1077 */
1078static int dyntick_save_progress_counter(struct rcu_data *rdp,
1079 bool *isidle, unsigned long *maxj)
1080{
1081 rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
1082 rcu_sysidle_check_cpu(rdp, isidle, maxj);
1083 if ((rdp->dynticks_snap & 0x1) == 0) {
1084 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1085 if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
1086 rdp->mynode->gpnum))
1087 WRITE_ONCE(rdp->gpwrap, true);
1088 return 1;
1089 }
1090 return 0;
1091}
1092
1093/*
1094 * Return true if the specified CPU has passed through a quiescent
1095 * state by virtue of being in or having passed through an dynticks
1096 * idle state since the last call to dyntick_save_progress_counter()
1097 * for this same CPU, or by virtue of having been offline.
1098 */
1099static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
1100 bool *isidle, unsigned long *maxj)
1101{
1102 unsigned int curr;
1103 int *rcrmp;
1104 unsigned int snap;
1105
1106 curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
1107 snap = (unsigned int)rdp->dynticks_snap;
1108
1109 /*
1110 * If the CPU passed through or entered a dynticks idle phase with
1111 * no active irq/NMI handlers, then we can safely pretend that the CPU
1112 * already acknowledged the request to pass through a quiescent
1113 * state. Either way, that CPU cannot possibly be in an RCU
1114 * read-side critical section that started before the beginning
1115 * of the current RCU grace period.
1116 */
1117 if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
1118 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1119 rdp->dynticks_fqs++;
1120 return 1;
1121 }
1122
1123 /*
1124 * Check for the CPU being offline, but only if the grace period
1125 * is old enough. We don't need to worry about the CPU changing
1126 * state: If we see it offline even once, it has been through a
1127 * quiescent state.
1128 *
1129 * The reason for insisting that the grace period be at least
1130 * one jiffy old is that CPUs that are not quite online and that
1131 * have just gone offline can still execute RCU read-side critical
1132 * sections.
1133 */
1134 if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
1135 return 0; /* Grace period is not old enough. */
1136 barrier();
1137 if (cpu_is_offline(rdp->cpu)) {
1138 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
1139 rdp->offline_fqs++;
1140 return 1;
1141 }
1142
1143 /*
1144 * A CPU running for an extended time within the kernel can
1145 * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode,
1146 * even context-switching back and forth between a pair of
1147 * in-kernel CPU-bound tasks cannot advance grace periods.
1148 * So if the grace period is old enough, make the CPU pay attention.
1149 * Note that the unsynchronized assignments to the per-CPU
1150 * rcu_sched_qs_mask variable are safe. Yes, setting of
1151 * bits can be lost, but they will be set again on the next
1152 * force-quiescent-state pass. So lost bit sets do not result
1153 * in incorrect behavior, merely in a grace period lasting
1154 * a few jiffies longer than it might otherwise. Because
1155 * there are at most four threads involved, and because the
1156 * updates are only once every few jiffies, the probability of
1157 * lossage (and thus of slight grace-period extension) is
1158 * quite low.
1159 *
1160 * Note that if the jiffies_till_sched_qs boot/sysfs parameter
1161 * is set too high, we override with half of the RCU CPU stall
1162 * warning delay.
1163 */
1164 rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
1165 if (ULONG_CMP_GE(jiffies,
1166 rdp->rsp->gp_start + jiffies_till_sched_qs) ||
1167 ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
1168 if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
1169 WRITE_ONCE(rdp->cond_resched_completed,
1170 READ_ONCE(rdp->mynode->completed));
1171 smp_mb(); /* ->cond_resched_completed before *rcrmp. */
1172 WRITE_ONCE(*rcrmp,
1173 READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
1174 }
1175 rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
1176 }
1177
1178 /* And if it has been a really long time, kick the CPU as well. */
1179 if (ULONG_CMP_GE(jiffies,
1180 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
1181 ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
1182 resched_cpu(rdp->cpu); /* Force CPU into scheduler. */
1183
1184 return 0;
1185}
1186
1187static void record_gp_stall_check_time(struct rcu_state *rsp)
1188{
1189 unsigned long j = jiffies;
1190 unsigned long j1;
1191
1192 rsp->gp_start = j;
1193 smp_wmb(); /* Record start time before stall time. */
1194 j1 = rcu_jiffies_till_stall_check();
1195 WRITE_ONCE(rsp->jiffies_stall, j + j1);
1196 rsp->jiffies_resched = j + j1 / 2;
1197 rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
1198}
1199
1200/*
1201 * Convert a ->gp_state value to a character string.
1202 */
1203static const char *gp_state_getname(short gs)
1204{
1205 if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
1206 return "???";
1207 return gp_state_names[gs];
1208}
1209
1210/*
1211 * Complain about starvation of grace-period kthread.
1212 */
1213static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
1214{
1215 unsigned long gpa;
1216 unsigned long j;
1217
1218 j = jiffies;
1219 gpa = READ_ONCE(rsp->gp_activity);
1220 if (j - gpa > 2 * HZ) {
1221 pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx\n",
1222 rsp->name, j - gpa,
1223 rsp->gpnum, rsp->completed,
1224 rsp->gp_flags,
1225 gp_state_getname(rsp->gp_state), rsp->gp_state,
1226 rsp->gp_kthread ? rsp->gp_kthread->state : ~0);
1227 if (rsp->gp_kthread)
1228 sched_show_task(rsp->gp_kthread);
1229 }
1230}
1231
1232/*
1233 * Dump stacks of all tasks running on stalled CPUs.
1234 */
1235static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
1236{
1237 int cpu;
1238 unsigned long flags;
1239 struct rcu_node *rnp;
1240
1241 rcu_for_each_leaf_node(rsp, rnp) {
1242 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1243 if (rnp->qsmask != 0) {
1244 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
1245 if (rnp->qsmask & (1UL << cpu))
1246 dump_cpu_task(rnp->grplo + cpu);
1247 }
1248 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1249 }
1250}
1251
1252static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
1253{
1254 int cpu;
1255 long delta;
1256 unsigned long flags;
1257 unsigned long gpa;
1258 unsigned long j;
1259 int ndetected = 0;
1260 struct rcu_node *rnp = rcu_get_root(rsp);
1261 long totqlen = 0;
1262
1263 /* Only let one CPU complain about others per time interval. */
1264
1265 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1266 delta = jiffies - READ_ONCE(rsp->jiffies_stall);
1267 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
1268 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1269 return;
1270 }
1271 WRITE_ONCE(rsp->jiffies_stall,
1272 jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1273 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1274
1275 /*
1276 * OK, time to rat on our buddy...
1277 * See Documentation/RCU/stallwarn.txt for info on how to debug
1278 * RCU CPU stall warnings.
1279 */
1280 pr_err("INFO: %s detected stalls on CPUs/tasks:",
1281 rsp->name);
1282 print_cpu_stall_info_begin();
1283 rcu_for_each_leaf_node(rsp, rnp) {
1284 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1285 ndetected += rcu_print_task_stall(rnp);
1286 if (rnp->qsmask != 0) {
1287 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
1288 if (rnp->qsmask & (1UL << cpu)) {
1289 print_cpu_stall_info(rsp,
1290 rnp->grplo + cpu);
1291 ndetected++;
1292 }
1293 }
1294 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1295 }
1296
1297 print_cpu_stall_info_end();
1298 for_each_possible_cpu(cpu)
1299 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1300 pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
1301 smp_processor_id(), (long)(jiffies - rsp->gp_start),
1302 (long)rsp->gpnum, (long)rsp->completed, totqlen);
1303 if (ndetected) {
1304 rcu_dump_cpu_stacks(rsp);
1305 } else {
1306 if (READ_ONCE(rsp->gpnum) != gpnum ||
1307 READ_ONCE(rsp->completed) == gpnum) {
1308 pr_err("INFO: Stall ended before state dump start\n");
1309 } else {
1310 j = jiffies;
1311 gpa = READ_ONCE(rsp->gp_activity);
1312 pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
1313 rsp->name, j - gpa, j, gpa,
1314 jiffies_till_next_fqs,
1315 rcu_get_root(rsp)->qsmask);
1316 /* In this case, the current CPU might be at fault. */
1317 sched_show_task(current);
1318 }
1319 }
1320
1321 /* Complain about tasks blocking the grace period. */
1322 rcu_print_detail_task_stall(rsp);
1323
1324 rcu_check_gp_kthread_starvation(rsp);
1325
1326 force_quiescent_state(rsp); /* Kick them all. */
1327}
1328
1329static void print_cpu_stall(struct rcu_state *rsp)
1330{
1331 int cpu;
1332 unsigned long flags;
1333 struct rcu_node *rnp = rcu_get_root(rsp);
1334 long totqlen = 0;
1335
1336 /*
1337 * OK, time to rat on ourselves...
1338 * See Documentation/RCU/stallwarn.txt for info on how to debug
1339 * RCU CPU stall warnings.
1340 */
1341 pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1342 print_cpu_stall_info_begin();
1343 print_cpu_stall_info(rsp, smp_processor_id());
1344 print_cpu_stall_info_end();
1345 for_each_possible_cpu(cpu)
1346 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1347 pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
1348 jiffies - rsp->gp_start,
1349 (long)rsp->gpnum, (long)rsp->completed, totqlen);
1350
1351 rcu_check_gp_kthread_starvation(rsp);
1352
1353 rcu_dump_cpu_stacks(rsp);
1354
1355 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1356 if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
1357 WRITE_ONCE(rsp->jiffies_stall,
1358 jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1359 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1360
1361 /*
1362 * Attempt to revive the RCU machinery by forcing a context switch.
1363 *
1364 * A context switch would normally allow the RCU state machine to make
1365 * progress and it could be we're stuck in kernel space without context
1366 * switches for an entirely unreasonable amount of time.
1367 */
1368 resched_cpu(smp_processor_id());
1369}
1370
1371static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
1372{
1373 unsigned long completed;
1374 unsigned long gpnum;
1375 unsigned long gps;
1376 unsigned long j;
1377 unsigned long js;
1378 struct rcu_node *rnp;
1379
1380 if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1381 return;
1382 j = jiffies;
1383
1384 /*
1385 * Lots of memory barriers to reject false positives.
1386 *
1387 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1388 * then rsp->gp_start, and finally rsp->completed. These values
1389 * are updated in the opposite order with memory barriers (or
1390 * equivalent) during grace-period initialization and cleanup.
1391 * Now, a false positive can occur if we get an new value of
1392 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
1393 * the memory barriers, the only way that this can happen is if one
1394 * grace period ends and another starts between these two fetches.
1395 * Detect this by comparing rsp->completed with the previous fetch
1396 * from rsp->gpnum.
1397 *
1398 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1399 * and rsp->gp_start suffice to forestall false positives.
1400 */
1401 gpnum = READ_ONCE(rsp->gpnum);
1402 smp_rmb(); /* Pick up ->gpnum first... */
1403 js = READ_ONCE(rsp->jiffies_stall);
1404 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1405 gps = READ_ONCE(rsp->gp_start);
1406 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1407 completed = READ_ONCE(rsp->completed);
1408 if (ULONG_CMP_GE(completed, gpnum) ||
1409 ULONG_CMP_LT(j, js) ||
1410 ULONG_CMP_GE(gps, js))
1411 return; /* No stall or GP completed since entering function. */
1412 rnp = rdp->mynode;
1413 if (rcu_gp_in_progress(rsp) &&
1414 (READ_ONCE(rnp->qsmask) & rdp->grpmask)) {
1415
1416 /* We haven't checked in, so go dump stack. */
1417 print_cpu_stall(rsp);
1418
1419 } else if (rcu_gp_in_progress(rsp) &&
1420 ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1421
1422 /* They had a few time units to dump stack, so complain. */
1423 print_other_cpu_stall(rsp, gpnum);
1424 }
1425}
1426
1427/**
1428 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1429 *
1430 * Set the stall-warning timeout way off into the future, thus preventing
1431 * any RCU CPU stall-warning messages from appearing in the current set of
1432 * RCU grace periods.
1433 *
1434 * The caller must disable hard irqs.
1435 */
1436void rcu_cpu_stall_reset(void)
1437{
1438 struct rcu_state *rsp;
1439
1440 for_each_rcu_flavor(rsp)
1441 WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
1442}
1443
1444/*
1445 * Initialize the specified rcu_data structure's default callback list
1446 * to empty. The default callback list is the one that is not used by
1447 * no-callbacks CPUs.
1448 */
1449static void init_default_callback_list(struct rcu_data *rdp)
1450{
1451 int i;
1452
1453 rdp->nxtlist = NULL;
1454 for (i = 0; i < RCU_NEXT_SIZE; i++)
1455 rdp->nxttail[i] = &rdp->nxtlist;
1456}
1457
1458/*
1459 * Initialize the specified rcu_data structure's callback list to empty.
1460 */
1461static void init_callback_list(struct rcu_data *rdp)
1462{
1463 if (init_nocb_callback_list(rdp))
1464 return;
1465 init_default_callback_list(rdp);
1466}
1467
1468/*
1469 * Determine the value that ->completed will have at the end of the
1470 * next subsequent grace period. This is used to tag callbacks so that
1471 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1472 * been dyntick-idle for an extended period with callbacks under the
1473 * influence of RCU_FAST_NO_HZ.
1474 *
1475 * The caller must hold rnp->lock with interrupts disabled.
1476 */
1477static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
1478 struct rcu_node *rnp)
1479{
1480 /*
1481 * If RCU is idle, we just wait for the next grace period.
1482 * But we can only be sure that RCU is idle if we are looking
1483 * at the root rcu_node structure -- otherwise, a new grace
1484 * period might have started, but just not yet gotten around
1485 * to initializing the current non-root rcu_node structure.
1486 */
1487 if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
1488 return rnp->completed + 1;
1489
1490 /*
1491 * Otherwise, wait for a possible partial grace period and
1492 * then the subsequent full grace period.
1493 */
1494 return rnp->completed + 2;
1495}
1496
1497/*
1498 * Trace-event helper function for rcu_start_future_gp() and
1499 * rcu_nocb_wait_gp().
1500 */
1501static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1502 unsigned long c, const char *s)
1503{
1504 trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
1505 rnp->completed, c, rnp->level,
1506 rnp->grplo, rnp->grphi, s);
1507}
1508
1509/*
1510 * Start some future grace period, as needed to handle newly arrived
1511 * callbacks. The required future grace periods are recorded in each
1512 * rcu_node structure's ->need_future_gp field. Returns true if there
1513 * is reason to awaken the grace-period kthread.
1514 *
1515 * The caller must hold the specified rcu_node structure's ->lock.
1516 */
1517static bool __maybe_unused
1518rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1519 unsigned long *c_out)
1520{
1521 unsigned long c;
1522 int i;
1523 bool ret = false;
1524 struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
1525
1526 /*
1527 * Pick up grace-period number for new callbacks. If this
1528 * grace period is already marked as needed, return to the caller.
1529 */
1530 c = rcu_cbs_completed(rdp->rsp, rnp);
1531 trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1532 if (rnp->need_future_gp[c & 0x1]) {
1533 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1534 goto out;
1535 }
1536
1537 /*
1538 * If either this rcu_node structure or the root rcu_node structure
1539 * believe that a grace period is in progress, then we must wait
1540 * for the one following, which is in "c". Because our request
1541 * will be noticed at the end of the current grace period, we don't
1542 * need to explicitly start one. We only do the lockless check
1543 * of rnp_root's fields if the current rcu_node structure thinks
1544 * there is no grace period in flight, and because we hold rnp->lock,
1545 * the only possible change is when rnp_root's two fields are
1546 * equal, in which case rnp_root->gpnum might be concurrently
1547 * incremented. But that is OK, as it will just result in our
1548 * doing some extra useless work.
1549 */
1550 if (rnp->gpnum != rnp->completed ||
1551 READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
1552 rnp->need_future_gp[c & 0x1]++;
1553 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1554 goto out;
1555 }
1556
1557 /*
1558 * There might be no grace period in progress. If we don't already
1559 * hold it, acquire the root rcu_node structure's lock in order to
1560 * start one (if needed).
1561 */
1562 if (rnp != rnp_root)
1563 raw_spin_lock_rcu_node(rnp_root);
1564
1565 /*
1566 * Get a new grace-period number. If there really is no grace
1567 * period in progress, it will be smaller than the one we obtained
1568 * earlier. Adjust callbacks as needed. Note that even no-CBs
1569 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1570 */
1571 c = rcu_cbs_completed(rdp->rsp, rnp_root);
1572 for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
1573 if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
1574 rdp->nxtcompleted[i] = c;
1575
1576 /*
1577 * If the needed for the required grace period is already
1578 * recorded, trace and leave.
1579 */
1580 if (rnp_root->need_future_gp[c & 0x1]) {
1581 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1582 goto unlock_out;
1583 }
1584
1585 /* Record the need for the future grace period. */
1586 rnp_root->need_future_gp[c & 0x1]++;
1587
1588 /* If a grace period is not already in progress, start one. */
1589 if (rnp_root->gpnum != rnp_root->completed) {
1590 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1591 } else {
1592 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1593 ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1594 }
1595unlock_out:
1596 if (rnp != rnp_root)
1597 raw_spin_unlock_rcu_node(rnp_root);
1598out:
1599 if (c_out != NULL)
1600 *c_out = c;
1601 return ret;
1602}
1603
1604/*
1605 * Clean up any old requests for the just-ended grace period. Also return
1606 * whether any additional grace periods have been requested. Also invoke
1607 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1608 * waiting for this grace period to complete.
1609 */
1610static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1611{
1612 int c = rnp->completed;
1613 int needmore;
1614 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1615
1616 rnp->need_future_gp[c & 0x1] = 0;
1617 needmore = rnp->need_future_gp[(c + 1) & 0x1];
1618 trace_rcu_future_gp(rnp, rdp, c,
1619 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1620 return needmore;
1621}
1622
1623/*
1624 * Awaken the grace-period kthread for the specified flavor of RCU.
1625 * Don't do a self-awaken, and don't bother awakening when there is
1626 * nothing for the grace-period kthread to do (as in several CPUs
1627 * raced to awaken, and we lost), and finally don't try to awaken
1628 * a kthread that has not yet been created.
1629 */
1630static void rcu_gp_kthread_wake(struct rcu_state *rsp)
1631{
1632 if (current == rsp->gp_kthread ||
1633 !READ_ONCE(rsp->gp_flags) ||
1634 !rsp->gp_kthread)
1635 return;
1636 swake_up(&rsp->gp_wq);
1637}
1638
1639/*
1640 * If there is room, assign a ->completed number to any callbacks on
1641 * this CPU that have not already been assigned. Also accelerate any
1642 * callbacks that were previously assigned a ->completed number that has
1643 * since proven to be too conservative, which can happen if callbacks get
1644 * assigned a ->completed number while RCU is idle, but with reference to
1645 * a non-root rcu_node structure. This function is idempotent, so it does
1646 * not hurt to call it repeatedly. Returns an flag saying that we should
1647 * awaken the RCU grace-period kthread.
1648 *
1649 * The caller must hold rnp->lock with interrupts disabled.
1650 */
1651static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1652 struct rcu_data *rdp)
1653{
1654 unsigned long c;
1655 int i;
1656 bool ret;
1657
1658 /* If the CPU has no callbacks, nothing to do. */
1659 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1660 return false;
1661
1662 /*
1663 * Starting from the sublist containing the callbacks most
1664 * recently assigned a ->completed number and working down, find the
1665 * first sublist that is not assignable to an upcoming grace period.
1666 * Such a sublist has something in it (first two tests) and has
1667 * a ->completed number assigned that will complete sooner than
1668 * the ->completed number for newly arrived callbacks (last test).
1669 *
1670 * The key point is that any later sublist can be assigned the
1671 * same ->completed number as the newly arrived callbacks, which
1672 * means that the callbacks in any of these later sublist can be
1673 * grouped into a single sublist, whether or not they have already
1674 * been assigned a ->completed number.
1675 */
1676 c = rcu_cbs_completed(rsp, rnp);
1677 for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
1678 if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
1679 !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
1680 break;
1681
1682 /*
1683 * If there are no sublist for unassigned callbacks, leave.
1684 * At the same time, advance "i" one sublist, so that "i" will
1685 * index into the sublist where all the remaining callbacks should
1686 * be grouped into.
1687 */
1688 if (++i >= RCU_NEXT_TAIL)
1689 return false;
1690
1691 /*
1692 * Assign all subsequent callbacks' ->completed number to the next
1693 * full grace period and group them all in the sublist initially
1694 * indexed by "i".
1695 */
1696 for (; i <= RCU_NEXT_TAIL; i++) {
1697 rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
1698 rdp->nxtcompleted[i] = c;
1699 }
1700 /* Record any needed additional grace periods. */
1701 ret = rcu_start_future_gp(rnp, rdp, NULL);
1702
1703 /* Trace depending on how much we were able to accelerate. */
1704 if (!*rdp->nxttail[RCU_WAIT_TAIL])
1705 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1706 else
1707 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1708 return ret;
1709}
1710
1711/*
1712 * Move any callbacks whose grace period has completed to the
1713 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1714 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1715 * sublist. This function is idempotent, so it does not hurt to
1716 * invoke it repeatedly. As long as it is not invoked -too- often...
1717 * Returns true if the RCU grace-period kthread needs to be awakened.
1718 *
1719 * The caller must hold rnp->lock with interrupts disabled.
1720 */
1721static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1722 struct rcu_data *rdp)
1723{
1724 int i, j;
1725
1726 /* If the CPU has no callbacks, nothing to do. */
1727 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1728 return false;
1729
1730 /*
1731 * Find all callbacks whose ->completed numbers indicate that they
1732 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1733 */
1734 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
1735 if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
1736 break;
1737 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
1738 }
1739 /* Clean up any sublist tail pointers that were misordered above. */
1740 for (j = RCU_WAIT_TAIL; j < i; j++)
1741 rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
1742
1743 /* Copy down callbacks to fill in empty sublists. */
1744 for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
1745 if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
1746 break;
1747 rdp->nxttail[j] = rdp->nxttail[i];
1748 rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
1749 }
1750
1751 /* Classify any remaining callbacks. */
1752 return rcu_accelerate_cbs(rsp, rnp, rdp);
1753}
1754
1755/*
1756 * Update CPU-local rcu_data state to record the beginnings and ends of
1757 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1758 * structure corresponding to the current CPU, and must have irqs disabled.
1759 * Returns true if the grace-period kthread needs to be awakened.
1760 */
1761static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
1762 struct rcu_data *rdp)
1763{
1764 bool ret;
1765
1766 /* Handle the ends of any preceding grace periods first. */
1767 if (rdp->completed == rnp->completed &&
1768 !unlikely(READ_ONCE(rdp->gpwrap))) {
1769
1770 /* No grace period end, so just accelerate recent callbacks. */
1771 ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1772
1773 } else {
1774
1775 /* Advance callbacks. */
1776 ret = rcu_advance_cbs(rsp, rnp, rdp);
1777
1778 /* Remember that we saw this grace-period completion. */
1779 rdp->completed = rnp->completed;
1780 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1781 }
1782
1783 if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
1784 /*
1785 * If the current grace period is waiting for this CPU,
1786 * set up to detect a quiescent state, otherwise don't
1787 * go looking for one.
1788 */
1789 rdp->gpnum = rnp->gpnum;
1790 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1791 rdp->cpu_no_qs.b.norm = true;
1792 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
1793 rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
1794 zero_cpu_stall_ticks(rdp);
1795 WRITE_ONCE(rdp->gpwrap, false);
1796 }
1797 return ret;
1798}
1799
1800static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1801{
1802 unsigned long flags;
1803 bool needwake;
1804 struct rcu_node *rnp;
1805
1806 local_irq_save(flags);
1807 rnp = rdp->mynode;
1808 if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
1809 rdp->completed == READ_ONCE(rnp->completed) &&
1810 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1811 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1812 local_irq_restore(flags);
1813 return;
1814 }
1815 needwake = __note_gp_changes(rsp, rnp, rdp);
1816 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1817 if (needwake)
1818 rcu_gp_kthread_wake(rsp);
1819}
1820
1821static void rcu_gp_slow(struct rcu_state *rsp, int delay)
1822{
1823 if (delay > 0 &&
1824 !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1825 schedule_timeout_uninterruptible(delay);
1826}
1827
1828/*
1829 * Initialize a new grace period. Return false if no grace period required.
1830 */
1831static bool rcu_gp_init(struct rcu_state *rsp)
1832{
1833 unsigned long oldmask;
1834 struct rcu_data *rdp;
1835 struct rcu_node *rnp = rcu_get_root(rsp);
1836
1837 WRITE_ONCE(rsp->gp_activity, jiffies);
1838 raw_spin_lock_irq_rcu_node(rnp);
1839 if (!READ_ONCE(rsp->gp_flags)) {
1840 /* Spurious wakeup, tell caller to go back to sleep. */
1841 raw_spin_unlock_irq_rcu_node(rnp);
1842 return false;
1843 }
1844 WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
1845
1846 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
1847 /*
1848 * Grace period already in progress, don't start another.
1849 * Not supposed to be able to happen.
1850 */
1851 raw_spin_unlock_irq_rcu_node(rnp);
1852 return false;
1853 }
1854
1855 /* Advance to a new grace period and initialize state. */
1856 record_gp_stall_check_time(rsp);
1857 /* Record GP times before starting GP, hence smp_store_release(). */
1858 smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1859 trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1860 raw_spin_unlock_irq_rcu_node(rnp);
1861
1862 /*
1863 * Apply per-leaf buffered online and offline operations to the
1864 * rcu_node tree. Note that this new grace period need not wait
1865 * for subsequent online CPUs, and that quiescent-state forcing
1866 * will handle subsequent offline CPUs.
1867 */
1868 rcu_for_each_leaf_node(rsp, rnp) {
1869 rcu_gp_slow(rsp, gp_preinit_delay);
1870 raw_spin_lock_irq_rcu_node(rnp);
1871 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1872 !rnp->wait_blkd_tasks) {
1873 /* Nothing to do on this leaf rcu_node structure. */
1874 raw_spin_unlock_irq_rcu_node(rnp);
1875 continue;
1876 }
1877
1878 /* Record old state, apply changes to ->qsmaskinit field. */
1879 oldmask = rnp->qsmaskinit;
1880 rnp->qsmaskinit = rnp->qsmaskinitnext;
1881
1882 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1883 if (!oldmask != !rnp->qsmaskinit) {
1884 if (!oldmask) /* First online CPU for this rcu_node. */
1885 rcu_init_new_rnp(rnp);
1886 else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
1887 rnp->wait_blkd_tasks = true;
1888 else /* Last offline CPU and can propagate. */
1889 rcu_cleanup_dead_rnp(rnp);
1890 }
1891
1892 /*
1893 * If all waited-on tasks from prior grace period are
1894 * done, and if all this rcu_node structure's CPUs are
1895 * still offline, propagate up the rcu_node tree and
1896 * clear ->wait_blkd_tasks. Otherwise, if one of this
1897 * rcu_node structure's CPUs has since come back online,
1898 * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
1899 * checks for this, so just call it unconditionally).
1900 */
1901 if (rnp->wait_blkd_tasks &&
1902 (!rcu_preempt_has_tasks(rnp) ||
1903 rnp->qsmaskinit)) {
1904 rnp->wait_blkd_tasks = false;
1905 rcu_cleanup_dead_rnp(rnp);
1906 }
1907
1908 raw_spin_unlock_irq_rcu_node(rnp);
1909 }
1910
1911 /*
1912 * Set the quiescent-state-needed bits in all the rcu_node
1913 * structures for all currently online CPUs in breadth-first order,
1914 * starting from the root rcu_node structure, relying on the layout
1915 * of the tree within the rsp->node[] array. Note that other CPUs
1916 * will access only the leaves of the hierarchy, thus seeing that no
1917 * grace period is in progress, at least until the corresponding
1918 * leaf node has been initialized. In addition, we have excluded
1919 * CPU-hotplug operations.
1920 *
1921 * The grace period cannot complete until the initialization
1922 * process finishes, because this kthread handles both.
1923 */
1924 rcu_for_each_node_breadth_first(rsp, rnp) {
1925 rcu_gp_slow(rsp, gp_init_delay);
1926 raw_spin_lock_irq_rcu_node(rnp);
1927 rdp = this_cpu_ptr(rsp->rda);
1928 rcu_preempt_check_blocked_tasks(rnp);
1929 rnp->qsmask = rnp->qsmaskinit;
1930 WRITE_ONCE(rnp->gpnum, rsp->gpnum);
1931 if (WARN_ON_ONCE(rnp->completed != rsp->completed))
1932 WRITE_ONCE(rnp->completed, rsp->completed);
1933 if (rnp == rdp->mynode)
1934 (void)__note_gp_changes(rsp, rnp, rdp);
1935 rcu_preempt_boost_start_gp(rnp);
1936 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
1937 rnp->level, rnp->grplo,
1938 rnp->grphi, rnp->qsmask);
1939 raw_spin_unlock_irq_rcu_node(rnp);
1940 cond_resched_rcu_qs();
1941 WRITE_ONCE(rsp->gp_activity, jiffies);
1942 }
1943
1944 return true;
1945}
1946
1947/*
1948 * Helper function for wait_event_interruptible_timeout() wakeup
1949 * at force-quiescent-state time.
1950 */
1951static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
1952{
1953 struct rcu_node *rnp = rcu_get_root(rsp);
1954
1955 /* Someone like call_rcu() requested a force-quiescent-state scan. */
1956 *gfp = READ_ONCE(rsp->gp_flags);
1957 if (*gfp & RCU_GP_FLAG_FQS)
1958 return true;
1959
1960 /* The current grace period has completed. */
1961 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
1962 return true;
1963
1964 return false;
1965}
1966
1967/*
1968 * Do one round of quiescent-state forcing.
1969 */
1970static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
1971{
1972 bool isidle = false;
1973 unsigned long maxj;
1974 struct rcu_node *rnp = rcu_get_root(rsp);
1975
1976 WRITE_ONCE(rsp->gp_activity, jiffies);
1977 rsp->n_force_qs++;
1978 if (first_time) {
1979 /* Collect dyntick-idle snapshots. */
1980 if (is_sysidle_rcu_state(rsp)) {
1981 isidle = true;
1982 maxj = jiffies - ULONG_MAX / 4;
1983 }
1984 force_qs_rnp(rsp, dyntick_save_progress_counter,
1985 &isidle, &maxj);
1986 rcu_sysidle_report_gp(rsp, isidle, maxj);
1987 } else {
1988 /* Handle dyntick-idle and offline CPUs. */
1989 isidle = true;
1990 force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1991 }
1992 /* Clear flag to prevent immediate re-entry. */
1993 if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
1994 raw_spin_lock_irq_rcu_node(rnp);
1995 WRITE_ONCE(rsp->gp_flags,
1996 READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
1997 raw_spin_unlock_irq_rcu_node(rnp);
1998 }
1999}
2000
2001/*
2002 * Clean up after the old grace period.
2003 */
2004static void rcu_gp_cleanup(struct rcu_state *rsp)
2005{
2006 unsigned long gp_duration;
2007 bool needgp = false;
2008 int nocb = 0;
2009 struct rcu_data *rdp;
2010 struct rcu_node *rnp = rcu_get_root(rsp);
2011 struct swait_queue_head *sq;
2012
2013 WRITE_ONCE(rsp->gp_activity, jiffies);
2014 raw_spin_lock_irq_rcu_node(rnp);
2015 gp_duration = jiffies - rsp->gp_start;
2016 if (gp_duration > rsp->gp_max)
2017 rsp->gp_max = gp_duration;
2018
2019 /*
2020 * We know the grace period is complete, but to everyone else
2021 * it appears to still be ongoing. But it is also the case
2022 * that to everyone else it looks like there is nothing that
2023 * they can do to advance the grace period. It is therefore
2024 * safe for us to drop the lock in order to mark the grace
2025 * period as completed in all of the rcu_node structures.
2026 */
2027 raw_spin_unlock_irq_rcu_node(rnp);
2028
2029 /*
2030 * Propagate new ->completed value to rcu_node structures so
2031 * that other CPUs don't have to wait until the start of the next
2032 * grace period to process their callbacks. This also avoids
2033 * some nasty RCU grace-period initialization races by forcing
2034 * the end of the current grace period to be completely recorded in
2035 * all of the rcu_node structures before the beginning of the next
2036 * grace period is recorded in any of the rcu_node structures.
2037 */
2038 rcu_for_each_node_breadth_first(rsp, rnp) {
2039 raw_spin_lock_irq_rcu_node(rnp);
2040 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
2041 WARN_ON_ONCE(rnp->qsmask);
2042 WRITE_ONCE(rnp->completed, rsp->gpnum);
2043 rdp = this_cpu_ptr(rsp->rda);
2044 if (rnp == rdp->mynode)
2045 needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
2046 /* smp_mb() provided by prior unlock-lock pair. */
2047 nocb += rcu_future_gp_cleanup(rsp, rnp);
2048 sq = rcu_nocb_gp_get(rnp);
2049 raw_spin_unlock_irq_rcu_node(rnp);
2050 rcu_nocb_gp_cleanup(sq);
2051 cond_resched_rcu_qs();
2052 WRITE_ONCE(rsp->gp_activity, jiffies);
2053 rcu_gp_slow(rsp, gp_cleanup_delay);
2054 }
2055 rnp = rcu_get_root(rsp);
2056 raw_spin_lock_irq_rcu_node(rnp); /* Order GP before ->completed update. */
2057 rcu_nocb_gp_set(rnp, nocb);
2058
2059 /* Declare grace period done. */
2060 WRITE_ONCE(rsp->completed, rsp->gpnum);
2061 trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
2062 rsp->gp_state = RCU_GP_IDLE;
2063 rdp = this_cpu_ptr(rsp->rda);
2064 /* Advance CBs to reduce false positives below. */
2065 needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
2066 if (needgp || cpu_needs_another_gp(rsp, rdp)) {
2067 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2068 trace_rcu_grace_period(rsp->name,
2069 READ_ONCE(rsp->gpnum),
2070 TPS("newreq"));
2071 }
2072 raw_spin_unlock_irq_rcu_node(rnp);
2073}
2074
2075/*
2076 * Body of kthread that handles grace periods.
2077 */
2078static int __noreturn rcu_gp_kthread(void *arg)
2079{
2080 bool first_gp_fqs;
2081 int gf;
2082 unsigned long j;
2083 int ret;
2084 struct rcu_state *rsp = arg;
2085 struct rcu_node *rnp = rcu_get_root(rsp);
2086
2087 rcu_bind_gp_kthread();
2088 for (;;) {
2089
2090 /* Handle grace-period start. */
2091 for (;;) {
2092 trace_rcu_grace_period(rsp->name,
2093 READ_ONCE(rsp->gpnum),
2094 TPS("reqwait"));
2095 rsp->gp_state = RCU_GP_WAIT_GPS;
2096 swait_event_interruptible(rsp->gp_wq,
2097 READ_ONCE(rsp->gp_flags) &
2098 RCU_GP_FLAG_INIT);
2099 rsp->gp_state = RCU_GP_DONE_GPS;
2100 /* Locking provides needed memory barrier. */
2101 if (rcu_gp_init(rsp))
2102 break;
2103 cond_resched_rcu_qs();
2104 WRITE_ONCE(rsp->gp_activity, jiffies);
2105 WARN_ON(signal_pending(current));
2106 trace_rcu_grace_period(rsp->name,
2107 READ_ONCE(rsp->gpnum),
2108 TPS("reqwaitsig"));
2109 }
2110
2111 /* Handle quiescent-state forcing. */
2112 first_gp_fqs = true;
2113 j = jiffies_till_first_fqs;
2114 if (j > HZ) {
2115 j = HZ;
2116 jiffies_till_first_fqs = HZ;
2117 }
2118 ret = 0;
2119 for (;;) {
2120 if (!ret)
2121 rsp->jiffies_force_qs = jiffies + j;
2122 trace_rcu_grace_period(rsp->name,
2123 READ_ONCE(rsp->gpnum),
2124 TPS("fqswait"));
2125 rsp->gp_state = RCU_GP_WAIT_FQS;
2126 ret = swait_event_interruptible_timeout(rsp->gp_wq,
2127 rcu_gp_fqs_check_wake(rsp, &gf), j);
2128 rsp->gp_state = RCU_GP_DOING_FQS;
2129 /* Locking provides needed memory barriers. */
2130 /* If grace period done, leave loop. */
2131 if (!READ_ONCE(rnp->qsmask) &&
2132 !rcu_preempt_blocked_readers_cgp(rnp))
2133 break;
2134 /* If time for quiescent-state forcing, do it. */
2135 if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
2136 (gf & RCU_GP_FLAG_FQS)) {
2137 trace_rcu_grace_period(rsp->name,
2138 READ_ONCE(rsp->gpnum),
2139 TPS("fqsstart"));
2140 rcu_gp_fqs(rsp, first_gp_fqs);
2141 first_gp_fqs = false;
2142 trace_rcu_grace_period(rsp->name,
2143 READ_ONCE(rsp->gpnum),
2144 TPS("fqsend"));
2145 cond_resched_rcu_qs();
2146 WRITE_ONCE(rsp->gp_activity, jiffies);
2147 } else {
2148 /* Deal with stray signal. */
2149 cond_resched_rcu_qs();
2150 WRITE_ONCE(rsp->gp_activity, jiffies);
2151 WARN_ON(signal_pending(current));
2152 trace_rcu_grace_period(rsp->name,
2153 READ_ONCE(rsp->gpnum),
2154 TPS("fqswaitsig"));
2155 }
2156 j = jiffies_till_next_fqs;
2157 if (j > HZ) {
2158 j = HZ;
2159 jiffies_till_next_fqs = HZ;
2160 } else if (j < 1) {
2161 j = 1;
2162 jiffies_till_next_fqs = 1;
2163 }
2164 }
2165
2166 /* Handle grace-period end. */
2167 rsp->gp_state = RCU_GP_CLEANUP;
2168 rcu_gp_cleanup(rsp);
2169 rsp->gp_state = RCU_GP_CLEANED;
2170 }
2171}
2172
2173/*
2174 * Start a new RCU grace period if warranted, re-initializing the hierarchy
2175 * in preparation for detecting the next grace period. The caller must hold
2176 * the root node's ->lock and hard irqs must be disabled.
2177 *
2178 * Note that it is legal for a dying CPU (which is marked as offline) to
2179 * invoke this function. This can happen when the dying CPU reports its
2180 * quiescent state.
2181 *
2182 * Returns true if the grace-period kthread must be awakened.
2183 */
2184static bool
2185rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
2186 struct rcu_data *rdp)
2187{
2188 if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
2189 /*
2190 * Either we have not yet spawned the grace-period
2191 * task, this CPU does not need another grace period,
2192 * or a grace period is already in progress.
2193 * Either way, don't start a new grace period.
2194 */
2195 return false;
2196 }
2197 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2198 trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
2199 TPS("newreq"));
2200
2201 /*
2202 * We can't do wakeups while holding the rnp->lock, as that
2203 * could cause possible deadlocks with the rq->lock. Defer
2204 * the wakeup to our caller.
2205 */
2206 return true;
2207}
2208
2209/*
2210 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
2211 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
2212 * is invoked indirectly from rcu_advance_cbs(), which would result in
2213 * endless recursion -- or would do so if it wasn't for the self-deadlock
2214 * that is encountered beforehand.
2215 *
2216 * Returns true if the grace-period kthread needs to be awakened.
2217 */
2218static bool rcu_start_gp(struct rcu_state *rsp)
2219{
2220 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
2221 struct rcu_node *rnp = rcu_get_root(rsp);
2222 bool ret = false;
2223
2224 /*
2225 * If there is no grace period in progress right now, any
2226 * callbacks we have up to this point will be satisfied by the
2227 * next grace period. Also, advancing the callbacks reduces the
2228 * probability of false positives from cpu_needs_another_gp()
2229 * resulting in pointless grace periods. So, advance callbacks
2230 * then start the grace period!
2231 */
2232 ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
2233 ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
2234 return ret;
2235}
2236
2237/*
2238 * Report a full set of quiescent states to the specified rcu_state data
2239 * structure. Invoke rcu_gp_kthread_wake() to awaken the grace-period
2240 * kthread if another grace period is required. Whether we wake
2241 * the grace-period kthread or it awakens itself for the next round
2242 * of quiescent-state forcing, that kthread will clean up after the
2243 * just-completed grace period. Note that the caller must hold rnp->lock,
2244 * which is released before return.
2245 */
2246static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
2247 __releases(rcu_get_root(rsp)->lock)
2248{
2249 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
2250 WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2251 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2252 swake_up(&rsp->gp_wq); /* Memory barrier implied by swake_up() path. */
2253}
2254
2255/*
2256 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
2257 * Allows quiescent states for a group of CPUs to be reported at one go
2258 * to the specified rcu_node structure, though all the CPUs in the group
2259 * must be represented by the same rcu_node structure (which need not be a
2260 * leaf rcu_node structure, though it often will be). The gps parameter
2261 * is the grace-period snapshot, which means that the quiescent states
2262 * are valid only if rnp->gpnum is equal to gps. That structure's lock
2263 * must be held upon entry, and it is released before return.
2264 */
2265static void
2266rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
2267 struct rcu_node *rnp, unsigned long gps, unsigned long flags)
2268 __releases(rnp->lock)
2269{
2270 unsigned long oldmask = 0;
2271 struct rcu_node *rnp_c;
2272
2273 /* Walk up the rcu_node hierarchy. */
2274 for (;;) {
2275 if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {
2276
2277 /*
2278 * Our bit has already been cleared, or the
2279 * relevant grace period is already over, so done.
2280 */
2281 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2282 return;
2283 }
2284 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
2285 rnp->qsmask &= ~mask;
2286 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
2287 mask, rnp->qsmask, rnp->level,
2288 rnp->grplo, rnp->grphi,
2289 !!rnp->gp_tasks);
2290 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2291
2292 /* Other bits still set at this level, so done. */
2293 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2294 return;
2295 }
2296 mask = rnp->grpmask;
2297 if (rnp->parent == NULL) {
2298
2299 /* No more levels. Exit loop holding root lock. */
2300
2301 break;
2302 }
2303 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2304 rnp_c = rnp;
2305 rnp = rnp->parent;
2306 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2307 oldmask = rnp_c->qsmask;
2308 }
2309
2310 /*
2311 * Get here if we are the last CPU to pass through a quiescent
2312 * state for this grace period. Invoke rcu_report_qs_rsp()
2313 * to clean up and start the next grace period if one is needed.
2314 */
2315 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2316}
2317
2318/*
2319 * Record a quiescent state for all tasks that were previously queued
2320 * on the specified rcu_node structure and that were blocking the current
2321 * RCU grace period. The caller must hold the specified rnp->lock with
2322 * irqs disabled, and this lock is released upon return, but irqs remain
2323 * disabled.
2324 */
2325static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
2326 struct rcu_node *rnp, unsigned long flags)
2327 __releases(rnp->lock)
2328{
2329 unsigned long gps;
2330 unsigned long mask;
2331 struct rcu_node *rnp_p;
2332
2333 if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
2334 rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2335 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2336 return; /* Still need more quiescent states! */
2337 }
2338
2339 rnp_p = rnp->parent;
2340 if (rnp_p == NULL) {
2341 /*
2342 * Only one rcu_node structure in the tree, so don't
2343 * try to report up to its nonexistent parent!
2344 */
2345 rcu_report_qs_rsp(rsp, flags);
2346 return;
2347 }
2348
2349 /* Report up the rest of the hierarchy, tracking current ->gpnum. */
2350 gps = rnp->gpnum;
2351 mask = rnp->grpmask;
2352 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2353 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
2354 rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
2355}
2356
2357/*
2358 * Record a quiescent state for the specified CPU to that CPU's rcu_data
2359 * structure. This must be called from the specified CPU.
2360 */
2361static void
2362rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2363{
2364 unsigned long flags;
2365 unsigned long mask;
2366 bool needwake;
2367 struct rcu_node *rnp;
2368
2369 rnp = rdp->mynode;
2370 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2371 if ((rdp->cpu_no_qs.b.norm &&
2372 rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) ||
2373 rdp->gpnum != rnp->gpnum || rnp->completed == rnp->gpnum ||
2374 rdp->gpwrap) {
2375
2376 /*
2377 * The grace period in which this quiescent state was
2378 * recorded has ended, so don't report it upwards.
2379 * We will instead need a new quiescent state that lies
2380 * within the current grace period.
2381 */
2382 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
2383 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
2384 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2385 return;
2386 }
2387 mask = rdp->grpmask;
2388 if ((rnp->qsmask & mask) == 0) {
2389 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2390 } else {
2391 rdp->core_needs_qs = false;
2392
2393 /*
2394 * This GP can't end until cpu checks in, so all of our
2395 * callbacks can be processed during the next GP.
2396 */
2397 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2398
2399 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2400 /* ^^^ Released rnp->lock */
2401 if (needwake)
2402 rcu_gp_kthread_wake(rsp);
2403 }
2404}
2405
2406/*
2407 * Check to see if there is a new grace period of which this CPU
2408 * is not yet aware, and if so, set up local rcu_data state for it.
2409 * Otherwise, see if this CPU has just passed through its first
2410 * quiescent state for this grace period, and record that fact if so.
2411 */
2412static void
2413rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
2414{
2415 /* Check for grace-period ends and beginnings. */
2416 note_gp_changes(rsp, rdp);
2417
2418 /*
2419 * Does this CPU still need to do its part for current grace period?
2420 * If no, return and let the other CPUs do their part as well.
2421 */
2422 if (!rdp->core_needs_qs)
2423 return;
2424
2425 /*
2426 * Was there a quiescent state since the beginning of the grace
2427 * period? If no, then exit and wait for the next call.
2428 */
2429 if (rdp->cpu_no_qs.b.norm &&
2430 rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr))
2431 return;
2432
2433 /*
2434 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2435 * judge of that).
2436 */
2437 rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2438}
2439
2440/*
2441 * Send the specified CPU's RCU callbacks to the orphanage. The
2442 * specified CPU must be offline, and the caller must hold the
2443 * ->orphan_lock.
2444 */
2445static void
2446rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
2447 struct rcu_node *rnp, struct rcu_data *rdp)
2448{
2449 /* No-CBs CPUs do not have orphanable callbacks. */
2450 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu))
2451 return;
2452
2453 /*
2454 * Orphan the callbacks. First adjust the counts. This is safe
2455 * because _rcu_barrier() excludes CPU-hotplug operations, so it
2456 * cannot be running now. Thus no memory barrier is required.
2457 */
2458 if (rdp->nxtlist != NULL) {
2459 rsp->qlen_lazy += rdp->qlen_lazy;
2460 rsp->qlen += rdp->qlen;
2461 rdp->n_cbs_orphaned += rdp->qlen;
2462 rdp->qlen_lazy = 0;
2463 WRITE_ONCE(rdp->qlen, 0);
2464 }
2465
2466 /*
2467 * Next, move those callbacks still needing a grace period to
2468 * the orphanage, where some other CPU will pick them up.
2469 * Some of the callbacks might have gone partway through a grace
2470 * period, but that is too bad. They get to start over because we
2471 * cannot assume that grace periods are synchronized across CPUs.
2472 * We don't bother updating the ->nxttail[] array yet, instead
2473 * we just reset the whole thing later on.
2474 */
2475 if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
2476 *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
2477 rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
2478 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2479 }
2480
2481 /*
2482 * Then move the ready-to-invoke callbacks to the orphanage,
2483 * where some other CPU will pick them up. These will not be
2484 * required to pass though another grace period: They are done.
2485 */
2486 if (rdp->nxtlist != NULL) {
2487 *rsp->orphan_donetail = rdp->nxtlist;
2488 rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
2489 }
2490
2491 /*
2492 * Finally, initialize the rcu_data structure's list to empty and
2493 * disallow further callbacks on this CPU.
2494 */
2495 init_callback_list(rdp);
2496 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2497}
2498
2499/*
2500 * Adopt the RCU callbacks from the specified rcu_state structure's
2501 * orphanage. The caller must hold the ->orphan_lock.
2502 */
2503static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
2504{
2505 int i;
2506 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2507
2508 /* No-CBs CPUs are handled specially. */
2509 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2510 rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
2511 return;
2512
2513 /* Do the accounting first. */
2514 rdp->qlen_lazy += rsp->qlen_lazy;
2515 rdp->qlen += rsp->qlen;
2516 rdp->n_cbs_adopted += rsp->qlen;
2517 if (rsp->qlen_lazy != rsp->qlen)
2518 rcu_idle_count_callbacks_posted();
2519 rsp->qlen_lazy = 0;
2520 rsp->qlen = 0;
2521
2522 /*
2523 * We do not need a memory barrier here because the only way we
2524 * can get here if there is an rcu_barrier() in flight is if
2525 * we are the task doing the rcu_barrier().
2526 */
2527
2528 /* First adopt the ready-to-invoke callbacks. */
2529 if (rsp->orphan_donelist != NULL) {
2530 *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
2531 *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
2532 for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
2533 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2534 rdp->nxttail[i] = rsp->orphan_donetail;
2535 rsp->orphan_donelist = NULL;
2536 rsp->orphan_donetail = &rsp->orphan_donelist;
2537 }
2538
2539 /* And then adopt the callbacks that still need a grace period. */
2540 if (rsp->orphan_nxtlist != NULL) {
2541 *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
2542 rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
2543 rsp->orphan_nxtlist = NULL;
2544 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2545 }
2546}
2547
2548/*
2549 * Trace the fact that this CPU is going offline.
2550 */
2551static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2552{
2553 RCU_TRACE(unsigned long mask);
2554 RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
2555 RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
2556
2557 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2558 return;
2559
2560 RCU_TRACE(mask = rdp->grpmask);
2561 trace_rcu_grace_period(rsp->name,
2562 rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2563 TPS("cpuofl"));
2564}
2565
2566/*
2567 * All CPUs for the specified rcu_node structure have gone offline,
2568 * and all tasks that were preempted within an RCU read-side critical
2569 * section while running on one of those CPUs have since exited their RCU
2570 * read-side critical section. Some other CPU is reporting this fact with
2571 * the specified rcu_node structure's ->lock held and interrupts disabled.
2572 * This function therefore goes up the tree of rcu_node structures,
2573 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
2574 * the leaf rcu_node structure's ->qsmaskinit field has already been
2575 * updated
2576 *
2577 * This function does check that the specified rcu_node structure has
2578 * all CPUs offline and no blocked tasks, so it is OK to invoke it
2579 * prematurely. That said, invoking it after the fact will cost you
2580 * a needless lock acquisition. So once it has done its work, don't
2581 * invoke it again.
2582 */
2583static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2584{
2585 long mask;
2586 struct rcu_node *rnp = rnp_leaf;
2587
2588 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2589 rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
2590 return;
2591 for (;;) {
2592 mask = rnp->grpmask;
2593 rnp = rnp->parent;
2594 if (!rnp)
2595 break;
2596 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2597 rnp->qsmaskinit &= ~mask;
2598 rnp->qsmask &= ~mask;
2599 if (rnp->qsmaskinit) {
2600 raw_spin_unlock_rcu_node(rnp);
2601 /* irqs remain disabled. */
2602 return;
2603 }
2604 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2605 }
2606}
2607
2608/*
2609 * The CPU has been completely removed, and some other CPU is reporting
2610 * this fact from process context. Do the remainder of the cleanup,
2611 * including orphaning the outgoing CPU's RCU callbacks, and also
2612 * adopting them. There can only be one CPU hotplug operation at a time,
2613 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2614 */
2615static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2616{
2617 unsigned long flags;
2618 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2619 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2620
2621 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2622 return;
2623
2624 /* Adjust any no-longer-needed kthreads. */
2625 rcu_boost_kthread_setaffinity(rnp, -1);
2626
2627 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2628 raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2629 rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2630 rcu_adopt_orphan_cbs(rsp, flags);
2631 raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
2632
2633 WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
2634 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2635 cpu, rdp->qlen, rdp->nxtlist);
2636}
2637
2638/*
2639 * Invoke any RCU callbacks that have made it to the end of their grace
2640 * period. Thottle as specified by rdp->blimit.
2641 */
2642static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2643{
2644 unsigned long flags;
2645 struct rcu_head *next, *list, **tail;
2646 long bl, count, count_lazy;
2647 int i;
2648
2649 /* If no callbacks are ready, just return. */
2650 if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2651 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2652 trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist),
2653 need_resched(), is_idle_task(current),
2654 rcu_is_callbacks_kthread());
2655 return;
2656 }
2657
2658 /*
2659 * Extract the list of ready callbacks, disabling to prevent
2660 * races with call_rcu() from interrupt handlers.
2661 */
2662 local_irq_save(flags);
2663 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2664 bl = rdp->blimit;
2665 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2666 list = rdp->nxtlist;
2667 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
2668 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2669 tail = rdp->nxttail[RCU_DONE_TAIL];
2670 for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
2671 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2672 rdp->nxttail[i] = &rdp->nxtlist;
2673 local_irq_restore(flags);
2674
2675 /* Invoke callbacks. */
2676 count = count_lazy = 0;
2677 while (list) {
2678 next = list->next;
2679 prefetch(next);
2680 debug_rcu_head_unqueue(list);
2681 if (__rcu_reclaim(rsp->name, list))
2682 count_lazy++;
2683 list = next;
2684 /* Stop only if limit reached and CPU has something to do. */
2685 if (++count >= bl &&
2686 (need_resched() ||
2687 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2688 break;
2689 }
2690
2691 local_irq_save(flags);
2692 trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
2693 is_idle_task(current),
2694 rcu_is_callbacks_kthread());
2695
2696 /* Update count, and requeue any remaining callbacks. */
2697 if (list != NULL) {
2698 *tail = rdp->nxtlist;
2699 rdp->nxtlist = list;
2700 for (i = 0; i < RCU_NEXT_SIZE; i++)
2701 if (&rdp->nxtlist == rdp->nxttail[i])
2702 rdp->nxttail[i] = tail;
2703 else
2704 break;
2705 }
2706 smp_mb(); /* List handling before counting for rcu_barrier(). */
2707 rdp->qlen_lazy -= count_lazy;
2708 WRITE_ONCE(rdp->qlen, rdp->qlen - count);
2709 rdp->n_cbs_invoked += count;
2710
2711 /* Reinstate batch limit if we have worked down the excess. */
2712 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
2713 rdp->blimit = blimit;
2714
2715 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2716 if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
2717 rdp->qlen_last_fqs_check = 0;
2718 rdp->n_force_qs_snap = rsp->n_force_qs;
2719 } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
2720 rdp->qlen_last_fqs_check = rdp->qlen;
2721 WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2722
2723 local_irq_restore(flags);
2724
2725 /* Re-invoke RCU core processing if there are callbacks remaining. */
2726 if (cpu_has_callbacks_ready_to_invoke(rdp))
2727 invoke_rcu_core();
2728}
2729
2730/*
2731 * Check to see if this CPU is in a non-context-switch quiescent state
2732 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2733 * Also schedule RCU core processing.
2734 *
2735 * This function must be called from hardirq context. It is normally
2736 * invoked from the scheduling-clock interrupt. If rcu_pending returns
2737 * false, there is no point in invoking rcu_check_callbacks().
2738 */
2739void rcu_check_callbacks(int user)
2740{
2741 trace_rcu_utilization(TPS("Start scheduler-tick"));
2742 increment_cpu_stall_ticks();
2743 if (user || rcu_is_cpu_rrupt_from_idle()) {
2744
2745 /*
2746 * Get here if this CPU took its interrupt from user
2747 * mode or from the idle loop, and if this is not a
2748 * nested interrupt. In this case, the CPU is in
2749 * a quiescent state, so note it.
2750 *
2751 * No memory barrier is required here because both
2752 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2753 * variables that other CPUs neither access nor modify,
2754 * at least not while the corresponding CPU is online.
2755 */
2756
2757 rcu_sched_qs();
2758 rcu_bh_qs();
2759
2760 } else if (!in_softirq()) {
2761
2762 /*
2763 * Get here if this CPU did not take its interrupt from
2764 * softirq, in other words, if it is not interrupting
2765 * a rcu_bh read-side critical section. This is an _bh
2766 * critical section, so note it.
2767 */
2768
2769 rcu_bh_qs();
2770 }
2771 rcu_preempt_check_callbacks();
2772 if (rcu_pending())
2773 invoke_rcu_core();
2774 if (user)
2775 rcu_note_voluntary_context_switch(current);
2776 trace_rcu_utilization(TPS("End scheduler-tick"));
2777}
2778
2779/*
2780 * Scan the leaf rcu_node structures, processing dyntick state for any that
2781 * have not yet encountered a quiescent state, using the function specified.
2782 * Also initiate boosting for any threads blocked on the root rcu_node.
2783 *
2784 * The caller must have suppressed start of new grace periods.
2785 */
2786static void force_qs_rnp(struct rcu_state *rsp,
2787 int (*f)(struct rcu_data *rsp, bool *isidle,
2788 unsigned long *maxj),
2789 bool *isidle, unsigned long *maxj)
2790{
2791 unsigned long bit;
2792 int cpu;
2793 unsigned long flags;
2794 unsigned long mask;
2795 struct rcu_node *rnp;
2796
2797 rcu_for_each_leaf_node(rsp, rnp) {
2798 cond_resched_rcu_qs();
2799 mask = 0;
2800 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2801 if (rnp->qsmask == 0) {
2802 if (rcu_state_p == &rcu_sched_state ||
2803 rsp != rcu_state_p ||
2804 rcu_preempt_blocked_readers_cgp(rnp)) {
2805 /*
2806 * No point in scanning bits because they
2807 * are all zero. But we might need to
2808 * priority-boost blocked readers.
2809 */
2810 rcu_initiate_boost(rnp, flags);
2811 /* rcu_initiate_boost() releases rnp->lock */
2812 continue;
2813 }
2814 if (rnp->parent &&
2815 (rnp->parent->qsmask & rnp->grpmask)) {
2816 /*
2817 * Race between grace-period
2818 * initialization and task exiting RCU
2819 * read-side critical section: Report.
2820 */
2821 rcu_report_unblock_qs_rnp(rsp, rnp, flags);
2822 /* rcu_report_unblock_qs_rnp() rlses ->lock */
2823 continue;
2824 }
2825 }
2826 cpu = rnp->grplo;
2827 bit = 1;
2828 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2829 if ((rnp->qsmask & bit) != 0) {
2830 if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
2831 mask |= bit;
2832 }
2833 }
2834 if (mask != 0) {
2835 /* Idle/offline CPUs, report (releases rnp->lock. */
2836 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2837 } else {
2838 /* Nothing to do here, so just drop the lock. */
2839 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2840 }
2841 }
2842}
2843
2844/*
2845 * Force quiescent states on reluctant CPUs, and also detect which
2846 * CPUs are in dyntick-idle mode.
2847 */
2848static void force_quiescent_state(struct rcu_state *rsp)
2849{
2850 unsigned long flags;
2851 bool ret;
2852 struct rcu_node *rnp;
2853 struct rcu_node *rnp_old = NULL;
2854
2855 /* Funnel through hierarchy to reduce memory contention. */
2856 rnp = __this_cpu_read(rsp->rda->mynode);
2857 for (; rnp != NULL; rnp = rnp->parent) {
2858 ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2859 !raw_spin_trylock(&rnp->fqslock);
2860 if (rnp_old != NULL)
2861 raw_spin_unlock(&rnp_old->fqslock);
2862 if (ret) {
2863 rsp->n_force_qs_lh++;
2864 return;
2865 }
2866 rnp_old = rnp;
2867 }
2868 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2869
2870 /* Reached the root of the rcu_node tree, acquire lock. */
2871 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2872 raw_spin_unlock(&rnp_old->fqslock);
2873 if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2874 rsp->n_force_qs_lh++;
2875 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2876 return; /* Someone beat us to it. */
2877 }
2878 WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2879 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2880 swake_up(&rsp->gp_wq); /* Memory barrier implied by swake_up() path. */
2881}
2882
2883/*
2884 * This does the RCU core processing work for the specified rcu_state
2885 * and rcu_data structures. This may be called only from the CPU to
2886 * whom the rdp belongs.
2887 */
2888static void
2889__rcu_process_callbacks(struct rcu_state *rsp)
2890{
2891 unsigned long flags;
2892 bool needwake;
2893 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2894
2895 WARN_ON_ONCE(rdp->beenonline == 0);
2896
2897 /* Update RCU state based on any recent quiescent states. */
2898 rcu_check_quiescent_state(rsp, rdp);
2899
2900 /* Does this CPU require a not-yet-started grace period? */
2901 local_irq_save(flags);
2902 if (cpu_needs_another_gp(rsp, rdp)) {
2903 raw_spin_lock_rcu_node(rcu_get_root(rsp)); /* irqs disabled. */
2904 needwake = rcu_start_gp(rsp);
2905 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2906 if (needwake)
2907 rcu_gp_kthread_wake(rsp);
2908 } else {
2909 local_irq_restore(flags);
2910 }
2911
2912 /* If there are callbacks ready, invoke them. */
2913 if (cpu_has_callbacks_ready_to_invoke(rdp))
2914 invoke_rcu_callbacks(rsp, rdp);
2915
2916 /* Do any needed deferred wakeups of rcuo kthreads. */
2917 do_nocb_deferred_wakeup(rdp);
2918}
2919
2920/*
2921 * Do RCU core processing for the current CPU.
2922 */
2923static void rcu_process_callbacks(struct softirq_action *unused)
2924{
2925 struct rcu_state *rsp;
2926
2927 if (cpu_is_offline(smp_processor_id()))
2928 return;
2929 trace_rcu_utilization(TPS("Start RCU core"));
2930 for_each_rcu_flavor(rsp)
2931 __rcu_process_callbacks(rsp);
2932 trace_rcu_utilization(TPS("End RCU core"));
2933}
2934
2935/*
2936 * Schedule RCU callback invocation. If the specified type of RCU
2937 * does not support RCU priority boosting, just do a direct call,
2938 * otherwise wake up the per-CPU kernel kthread. Note that because we
2939 * are running on the current CPU with softirqs disabled, the
2940 * rcu_cpu_kthread_task cannot disappear out from under us.
2941 */
2942static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2943{
2944 if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
2945 return;
2946 if (likely(!rsp->boost)) {
2947 rcu_do_batch(rsp, rdp);
2948 return;
2949 }
2950 invoke_rcu_callbacks_kthread();
2951}
2952
2953static void invoke_rcu_core(void)
2954{
2955 if (cpu_online(smp_processor_id()))
2956 raise_softirq(RCU_SOFTIRQ);
2957}
2958
2959/*
2960 * Handle any core-RCU processing required by a call_rcu() invocation.
2961 */
2962static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
2963 struct rcu_head *head, unsigned long flags)
2964{
2965 bool needwake;
2966
2967 /*
2968 * If called from an extended quiescent state, invoke the RCU
2969 * core in order to force a re-evaluation of RCU's idleness.
2970 */
2971 if (!rcu_is_watching())
2972 invoke_rcu_core();
2973
2974 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2975 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2976 return;
2977
2978 /*
2979 * Force the grace period if too many callbacks or too long waiting.
2980 * Enforce hysteresis, and don't invoke force_quiescent_state()
2981 * if some other CPU has recently done so. Also, don't bother
2982 * invoking force_quiescent_state() if the newly enqueued callback
2983 * is the only one waiting for a grace period to complete.
2984 */
2985 if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2986
2987 /* Are we ignoring a completed grace period? */
2988 note_gp_changes(rsp, rdp);
2989
2990 /* Start a new grace period if one not already started. */
2991 if (!rcu_gp_in_progress(rsp)) {
2992 struct rcu_node *rnp_root = rcu_get_root(rsp);
2993
2994 raw_spin_lock_rcu_node(rnp_root);
2995 needwake = rcu_start_gp(rsp);
2996 raw_spin_unlock_rcu_node(rnp_root);
2997 if (needwake)
2998 rcu_gp_kthread_wake(rsp);
2999 } else {
3000 /* Give the grace period a kick. */
3001 rdp->blimit = LONG_MAX;
3002 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
3003 *rdp->nxttail[RCU_DONE_TAIL] != head)
3004 force_quiescent_state(rsp);
3005 rdp->n_force_qs_snap = rsp->n_force_qs;
3006 rdp->qlen_last_fqs_check = rdp->qlen;
3007 }
3008 }
3009}
3010
3011/*
3012 * RCU callback function to leak a callback.
3013 */
3014static void rcu_leak_callback(struct rcu_head *rhp)
3015{
3016}
3017
3018/*
3019 * Helper function for call_rcu() and friends. The cpu argument will
3020 * normally be -1, indicating "currently running CPU". It may specify
3021 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
3022 * is expected to specify a CPU.
3023 */
3024static void
3025__call_rcu(struct rcu_head *head, rcu_callback_t func,
3026 struct rcu_state *rsp, int cpu, bool lazy)
3027{
3028 unsigned long flags;
3029 struct rcu_data *rdp;
3030
3031 WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */
3032 if (debug_rcu_head_queue(head)) {
3033 /* Probable double call_rcu(), so leak the callback. */
3034 WRITE_ONCE(head->func, rcu_leak_callback);
3035 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
3036 return;
3037 }
3038 head->func = func;
3039 head->next = NULL;
3040
3041 /*
3042 * Opportunistically note grace-period endings and beginnings.
3043 * Note that we might see a beginning right after we see an
3044 * end, but never vice versa, since this CPU has to pass through
3045 * a quiescent state betweentimes.
3046 */
3047 local_irq_save(flags);
3048 rdp = this_cpu_ptr(rsp->rda);
3049
3050 /* Add the callback to our list. */
3051 if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
3052 int offline;
3053
3054 if (cpu != -1)
3055 rdp = per_cpu_ptr(rsp->rda, cpu);
3056 if (likely(rdp->mynode)) {
3057 /* Post-boot, so this should be for a no-CBs CPU. */
3058 offline = !__call_rcu_nocb(rdp, head, lazy, flags);
3059 WARN_ON_ONCE(offline);
3060 /* Offline CPU, _call_rcu() illegal, leak callback. */
3061 local_irq_restore(flags);
3062 return;
3063 }
3064 /*
3065 * Very early boot, before rcu_init(). Initialize if needed
3066 * and then drop through to queue the callback.
3067 */
3068 BUG_ON(cpu != -1);
3069 WARN_ON_ONCE(!rcu_is_watching());
3070 if (!likely(rdp->nxtlist))
3071 init_default_callback_list(rdp);
3072 }
3073 WRITE_ONCE(rdp->qlen, rdp->qlen + 1);
3074 if (lazy)
3075 rdp->qlen_lazy++;
3076 else
3077 rcu_idle_count_callbacks_posted();
3078 smp_mb(); /* Count before adding callback for rcu_barrier(). */
3079 *rdp->nxttail[RCU_NEXT_TAIL] = head;
3080 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
3081
3082 if (__is_kfree_rcu_offset((unsigned long)func))
3083 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
3084 rdp->qlen_lazy, rdp->qlen);
3085 else
3086 trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
3087
3088 /* Go handle any RCU core processing required. */
3089 __call_rcu_core(rsp, rdp, head, flags);
3090 local_irq_restore(flags);
3091}
3092
3093/*
3094 * Queue an RCU-sched callback for invocation after a grace period.
3095 */
3096void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
3097{
3098 __call_rcu(head, func, &rcu_sched_state, -1, 0);
3099}
3100EXPORT_SYMBOL_GPL(call_rcu_sched);
3101
3102/*
3103 * Queue an RCU callback for invocation after a quicker grace period.
3104 */
3105void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
3106{
3107 __call_rcu(head, func, &rcu_bh_state, -1, 0);
3108}
3109EXPORT_SYMBOL_GPL(call_rcu_bh);
3110
3111/*
3112 * Queue an RCU callback for lazy invocation after a grace period.
3113 * This will likely be later named something like "call_rcu_lazy()",
3114 * but this change will require some way of tagging the lazy RCU
3115 * callbacks in the list of pending callbacks. Until then, this
3116 * function may only be called from __kfree_rcu().
3117 */
3118void kfree_call_rcu(struct rcu_head *head,
3119 rcu_callback_t func)
3120{
3121 __call_rcu(head, func, rcu_state_p, -1, 1);
3122}
3123EXPORT_SYMBOL_GPL(kfree_call_rcu);
3124
3125/*
3126 * Because a context switch is a grace period for RCU-sched and RCU-bh,
3127 * any blocking grace-period wait automatically implies a grace period
3128 * if there is only one CPU online at any point time during execution
3129 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
3130 * occasionally incorrectly indicate that there are multiple CPUs online
3131 * when there was in fact only one the whole time, as this just adds
3132 * some overhead: RCU still operates correctly.
3133 */
3134static inline int rcu_blocking_is_gp(void)
3135{
3136 int ret;
3137
3138 might_sleep(); /* Check for RCU read-side critical section. */
3139 preempt_disable();
3140 ret = num_online_cpus() <= 1;
3141 preempt_enable();
3142 return ret;
3143}
3144
3145/**
3146 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
3147 *
3148 * Control will return to the caller some time after a full rcu-sched
3149 * grace period has elapsed, in other words after all currently executing
3150 * rcu-sched read-side critical sections have completed. These read-side
3151 * critical sections are delimited by rcu_read_lock_sched() and
3152 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
3153 * local_irq_disable(), and so on may be used in place of
3154 * rcu_read_lock_sched().
3155 *
3156 * This means that all preempt_disable code sequences, including NMI and
3157 * non-threaded hardware-interrupt handlers, in progress on entry will
3158 * have completed before this primitive returns. However, this does not
3159 * guarantee that softirq handlers will have completed, since in some
3160 * kernels, these handlers can run in process context, and can block.
3161 *
3162 * Note that this guarantee implies further memory-ordering guarantees.
3163 * On systems with more than one CPU, when synchronize_sched() returns,
3164 * each CPU is guaranteed to have executed a full memory barrier since the
3165 * end of its last RCU-sched read-side critical section whose beginning
3166 * preceded the call to synchronize_sched(). In addition, each CPU having
3167 * an RCU read-side critical section that extends beyond the return from
3168 * synchronize_sched() is guaranteed to have executed a full memory barrier
3169 * after the beginning of synchronize_sched() and before the beginning of
3170 * that RCU read-side critical section. Note that these guarantees include
3171 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3172 * that are executing in the kernel.
3173 *
3174 * Furthermore, if CPU A invoked synchronize_sched(), which returned
3175 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3176 * to have executed a full memory barrier during the execution of
3177 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
3178 * again only if the system has more than one CPU).
3179 *
3180 * This primitive provides the guarantees made by the (now removed)
3181 * synchronize_kernel() API. In contrast, synchronize_rcu() only
3182 * guarantees that rcu_read_lock() sections will have completed.
3183 * In "classic RCU", these two guarantees happen to be one and
3184 * the same, but can differ in realtime RCU implementations.
3185 */
3186void synchronize_sched(void)
3187{
3188 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3189 lock_is_held(&rcu_lock_map) ||
3190 lock_is_held(&rcu_sched_lock_map),
3191 "Illegal synchronize_sched() in RCU-sched read-side critical section");
3192 if (rcu_blocking_is_gp())
3193 return;
3194 if (rcu_gp_is_expedited())
3195 synchronize_sched_expedited();
3196 else
3197 wait_rcu_gp(call_rcu_sched);
3198}
3199EXPORT_SYMBOL_GPL(synchronize_sched);
3200
3201/**
3202 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
3203 *
3204 * Control will return to the caller some time after a full rcu_bh grace
3205 * period has elapsed, in other words after all currently executing rcu_bh
3206 * read-side critical sections have completed. RCU read-side critical
3207 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
3208 * and may be nested.
3209 *
3210 * See the description of synchronize_sched() for more detailed information
3211 * on memory ordering guarantees.
3212 */
3213void synchronize_rcu_bh(void)
3214{
3215 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3216 lock_is_held(&rcu_lock_map) ||
3217 lock_is_held(&rcu_sched_lock_map),
3218 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
3219 if (rcu_blocking_is_gp())
3220 return;
3221 if (rcu_gp_is_expedited())
3222 synchronize_rcu_bh_expedited();
3223 else
3224 wait_rcu_gp(call_rcu_bh);
3225}
3226EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
3227
3228/**
3229 * get_state_synchronize_rcu - Snapshot current RCU state
3230 *
3231 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3232 * to determine whether or not a full grace period has elapsed in the
3233 * meantime.
3234 */
3235unsigned long get_state_synchronize_rcu(void)
3236{
3237 /*
3238 * Any prior manipulation of RCU-protected data must happen
3239 * before the load from ->gpnum.
3240 */
3241 smp_mb(); /* ^^^ */
3242
3243 /*
3244 * Make sure this load happens before the purportedly
3245 * time-consuming work between get_state_synchronize_rcu()
3246 * and cond_synchronize_rcu().
3247 */
3248 return smp_load_acquire(&rcu_state_p->gpnum);
3249}
3250EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3251
3252/**
3253 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3254 *
3255 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
3256 *
3257 * If a full RCU grace period has elapsed since the earlier call to
3258 * get_state_synchronize_rcu(), just return. Otherwise, invoke
3259 * synchronize_rcu() to wait for a full grace period.
3260 *
3261 * Yes, this function does not take counter wrap into account. But
3262 * counter wrap is harmless. If the counter wraps, we have waited for
3263 * more than 2 billion grace periods (and way more on a 64-bit system!),
3264 * so waiting for one additional grace period should be just fine.
3265 */
3266void cond_synchronize_rcu(unsigned long oldstate)
3267{
3268 unsigned long newstate;
3269
3270 /*
3271 * Ensure that this load happens before any RCU-destructive
3272 * actions the caller might carry out after we return.
3273 */
3274 newstate = smp_load_acquire(&rcu_state_p->completed);
3275 if (ULONG_CMP_GE(oldstate, newstate))
3276 synchronize_rcu();
3277}
3278EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3279
3280/**
3281 * get_state_synchronize_sched - Snapshot current RCU-sched state
3282 *
3283 * Returns a cookie that is used by a later call to cond_synchronize_sched()
3284 * to determine whether or not a full grace period has elapsed in the
3285 * meantime.
3286 */
3287unsigned long get_state_synchronize_sched(void)
3288{
3289 /*
3290 * Any prior manipulation of RCU-protected data must happen
3291 * before the load from ->gpnum.
3292 */
3293 smp_mb(); /* ^^^ */
3294
3295 /*
3296 * Make sure this load happens before the purportedly
3297 * time-consuming work between get_state_synchronize_sched()
3298 * and cond_synchronize_sched().
3299 */
3300 return smp_load_acquire(&rcu_sched_state.gpnum);
3301}
3302EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
3303
3304/**
3305 * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
3306 *
3307 * @oldstate: return value from earlier call to get_state_synchronize_sched()
3308 *
3309 * If a full RCU-sched grace period has elapsed since the earlier call to
3310 * get_state_synchronize_sched(), just return. Otherwise, invoke
3311 * synchronize_sched() to wait for a full grace period.
3312 *
3313 * Yes, this function does not take counter wrap into account. But
3314 * counter wrap is harmless. If the counter wraps, we have waited for
3315 * more than 2 billion grace periods (and way more on a 64-bit system!),
3316 * so waiting for one additional grace period should be just fine.
3317 */
3318void cond_synchronize_sched(unsigned long oldstate)
3319{
3320 unsigned long newstate;
3321
3322 /*
3323 * Ensure that this load happens before any RCU-destructive
3324 * actions the caller might carry out after we return.
3325 */
3326 newstate = smp_load_acquire(&rcu_sched_state.completed);
3327 if (ULONG_CMP_GE(oldstate, newstate))
3328 synchronize_sched();
3329}
3330EXPORT_SYMBOL_GPL(cond_synchronize_sched);
3331
3332/* Adjust sequence number for start of update-side operation. */
3333static void rcu_seq_start(unsigned long *sp)
3334{
3335 WRITE_ONCE(*sp, *sp + 1);
3336 smp_mb(); /* Ensure update-side operation after counter increment. */
3337 WARN_ON_ONCE(!(*sp & 0x1));
3338}
3339
3340/* Adjust sequence number for end of update-side operation. */
3341static void rcu_seq_end(unsigned long *sp)
3342{
3343 smp_mb(); /* Ensure update-side operation before counter increment. */
3344 WRITE_ONCE(*sp, *sp + 1);
3345 WARN_ON_ONCE(*sp & 0x1);
3346}
3347
3348/* Take a snapshot of the update side's sequence number. */
3349static unsigned long rcu_seq_snap(unsigned long *sp)
3350{
3351 unsigned long s;
3352
3353 s = (READ_ONCE(*sp) + 3) & ~0x1;
3354 smp_mb(); /* Above access must not bleed into critical section. */
3355 return s;
3356}
3357
3358/*
3359 * Given a snapshot from rcu_seq_snap(), determine whether or not a
3360 * full update-side operation has occurred.
3361 */
3362static bool rcu_seq_done(unsigned long *sp, unsigned long s)
3363{
3364 return ULONG_CMP_GE(READ_ONCE(*sp), s);
3365}
3366
3367/* Wrapper functions for expedited grace periods. */
3368static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
3369{
3370 rcu_seq_start(&rsp->expedited_sequence);
3371}
3372static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
3373{
3374 rcu_seq_end(&rsp->expedited_sequence);
3375 smp_mb(); /* Ensure that consecutive grace periods serialize. */
3376}
3377static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
3378{
3379 smp_mb(); /* Caller's modifications seen first by other CPUs. */
3380 return rcu_seq_snap(&rsp->expedited_sequence);
3381}
3382static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
3383{
3384 return rcu_seq_done(&rsp->expedited_sequence, s);
3385}
3386
3387/*
3388 * Reset the ->expmaskinit values in the rcu_node tree to reflect any
3389 * recent CPU-online activity. Note that these masks are not cleared
3390 * when CPUs go offline, so they reflect the union of all CPUs that have
3391 * ever been online. This means that this function normally takes its
3392 * no-work-to-do fastpath.
3393 */
3394static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
3395{
3396 bool done;
3397 unsigned long flags;
3398 unsigned long mask;
3399 unsigned long oldmask;
3400 int ncpus = READ_ONCE(rsp->ncpus);
3401 struct rcu_node *rnp;
3402 struct rcu_node *rnp_up;
3403
3404 /* If no new CPUs onlined since last time, nothing to do. */
3405 if (likely(ncpus == rsp->ncpus_snap))
3406 return;
3407 rsp->ncpus_snap = ncpus;
3408
3409 /*
3410 * Each pass through the following loop propagates newly onlined
3411 * CPUs for the current rcu_node structure up the rcu_node tree.
3412 */
3413 rcu_for_each_leaf_node(rsp, rnp) {
3414 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3415 if (rnp->expmaskinit == rnp->expmaskinitnext) {
3416 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3417 continue; /* No new CPUs, nothing to do. */
3418 }
3419
3420 /* Update this node's mask, track old value for propagation. */
3421 oldmask = rnp->expmaskinit;
3422 rnp->expmaskinit = rnp->expmaskinitnext;
3423 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3424
3425 /* If was already nonzero, nothing to propagate. */
3426 if (oldmask)
3427 continue;
3428
3429 /* Propagate the new CPU up the tree. */
3430 mask = rnp->grpmask;
3431 rnp_up = rnp->parent;
3432 done = false;
3433 while (rnp_up) {
3434 raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
3435 if (rnp_up->expmaskinit)
3436 done = true;
3437 rnp_up->expmaskinit |= mask;
3438 raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
3439 if (done)
3440 break;
3441 mask = rnp_up->grpmask;
3442 rnp_up = rnp_up->parent;
3443 }
3444 }
3445}
3446
3447/*
3448 * Reset the ->expmask values in the rcu_node tree in preparation for
3449 * a new expedited grace period.
3450 */
3451static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
3452{
3453 unsigned long flags;
3454 struct rcu_node *rnp;
3455
3456 sync_exp_reset_tree_hotplug(rsp);
3457 rcu_for_each_node_breadth_first(rsp, rnp) {
3458 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3459 WARN_ON_ONCE(rnp->expmask);
3460 rnp->expmask = rnp->expmaskinit;
3461 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3462 }
3463}
3464
3465/*
3466 * Return non-zero if there is no RCU expedited grace period in progress
3467 * for the specified rcu_node structure, in other words, if all CPUs and
3468 * tasks covered by the specified rcu_node structure have done their bit
3469 * for the current expedited grace period. Works only for preemptible
3470 * RCU -- other RCU implementation use other means.
3471 *
3472 * Caller must hold the root rcu_node's exp_funnel_mutex.
3473 */
3474static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
3475{
3476 return rnp->exp_tasks == NULL &&
3477 READ_ONCE(rnp->expmask) == 0;
3478}
3479
3480/*
3481 * Report the exit from RCU read-side critical section for the last task
3482 * that queued itself during or before the current expedited preemptible-RCU
3483 * grace period. This event is reported either to the rcu_node structure on
3484 * which the task was queued or to one of that rcu_node structure's ancestors,
3485 * recursively up the tree. (Calm down, calm down, we do the recursion
3486 * iteratively!)
3487 *
3488 * Caller must hold the root rcu_node's exp_funnel_mutex and the
3489 * specified rcu_node structure's ->lock.
3490 */
3491static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
3492 bool wake, unsigned long flags)
3493 __releases(rnp->lock)
3494{
3495 unsigned long mask;
3496
3497 for (;;) {
3498 if (!sync_rcu_preempt_exp_done(rnp)) {
3499 if (!rnp->expmask)
3500 rcu_initiate_boost(rnp, flags);
3501 else
3502 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3503 break;
3504 }
3505 if (rnp->parent == NULL) {
3506 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3507 if (wake) {
3508 smp_mb(); /* EGP done before wake_up(). */
3509 swake_up(&rsp->expedited_wq);
3510 }
3511 break;
3512 }
3513 mask = rnp->grpmask;
3514 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
3515 rnp = rnp->parent;
3516 raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
3517 WARN_ON_ONCE(!(rnp->expmask & mask));
3518 rnp->expmask &= ~mask;
3519 }
3520}
3521
3522/*
3523 * Report expedited quiescent state for specified node. This is a
3524 * lock-acquisition wrapper function for __rcu_report_exp_rnp().
3525 *
3526 * Caller must hold the root rcu_node's exp_funnel_mutex.
3527 */
3528static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
3529 struct rcu_node *rnp, bool wake)
3530{
3531 unsigned long flags;
3532
3533 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3534 __rcu_report_exp_rnp(rsp, rnp, wake, flags);
3535}
3536
3537/*
3538 * Report expedited quiescent state for multiple CPUs, all covered by the
3539 * specified leaf rcu_node structure. Caller must hold the root
3540 * rcu_node's exp_funnel_mutex.
3541 */
3542static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
3543 unsigned long mask, bool wake)
3544{
3545 unsigned long flags;
3546
3547 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3548 if (!(rnp->expmask & mask)) {
3549 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3550 return;
3551 }
3552 rnp->expmask &= ~mask;
3553 __rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
3554}
3555
3556/*
3557 * Report expedited quiescent state for specified rcu_data (CPU).
3558 * Caller must hold the root rcu_node's exp_funnel_mutex.
3559 */
3560static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
3561 bool wake)
3562{
3563 rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
3564}
3565
3566/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
3567static bool sync_exp_work_done(struct rcu_state *rsp, struct rcu_node *rnp,
3568 struct rcu_data *rdp,
3569 atomic_long_t *stat, unsigned long s)
3570{
3571 if (rcu_exp_gp_seq_done(rsp, s)) {
3572 if (rnp)
3573 mutex_unlock(&rnp->exp_funnel_mutex);
3574 else if (rdp)
3575 mutex_unlock(&rdp->exp_funnel_mutex);
3576 /* Ensure test happens before caller kfree(). */
3577 smp_mb__before_atomic(); /* ^^^ */
3578 atomic_long_inc(stat);
3579 return true;
3580 }
3581 return false;
3582}
3583
3584/*
3585 * Funnel-lock acquisition for expedited grace periods. Returns a
3586 * pointer to the root rcu_node structure, or NULL if some other
3587 * task did the expedited grace period for us.
3588 */
3589static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
3590{
3591 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
3592 struct rcu_node *rnp0;
3593 struct rcu_node *rnp1 = NULL;
3594
3595 /*
3596 * First try directly acquiring the root lock in order to reduce
3597 * latency in the common case where expedited grace periods are
3598 * rare. We check mutex_is_locked() to avoid pathological levels of
3599 * memory contention on ->exp_funnel_mutex in the heavy-load case.
3600 */
3601 rnp0 = rcu_get_root(rsp);
3602 if (!mutex_is_locked(&rnp0->exp_funnel_mutex)) {
3603 if (mutex_trylock(&rnp0->exp_funnel_mutex)) {
3604 if (sync_exp_work_done(rsp, rnp0, NULL,
3605 &rdp->expedited_workdone0, s))
3606 return NULL;
3607 return rnp0;
3608 }
3609 }
3610
3611 /*
3612 * Each pass through the following loop works its way
3613 * up the rcu_node tree, returning if others have done the
3614 * work or otherwise falls through holding the root rnp's
3615 * ->exp_funnel_mutex. The mapping from CPU to rcu_node structure
3616 * can be inexact, as it is just promoting locality and is not
3617 * strictly needed for correctness.
3618 */
3619 if (sync_exp_work_done(rsp, NULL, NULL, &rdp->expedited_workdone1, s))
3620 return NULL;
3621 mutex_lock(&rdp->exp_funnel_mutex);
3622 rnp0 = rdp->mynode;
3623 for (; rnp0 != NULL; rnp0 = rnp0->parent) {
3624 if (sync_exp_work_done(rsp, rnp1, rdp,
3625 &rdp->expedited_workdone2, s))
3626 return NULL;
3627 mutex_lock(&rnp0->exp_funnel_mutex);
3628 if (rnp1)
3629 mutex_unlock(&rnp1->exp_funnel_mutex);
3630 else
3631 mutex_unlock(&rdp->exp_funnel_mutex);
3632 rnp1 = rnp0;
3633 }
3634 if (sync_exp_work_done(rsp, rnp1, rdp,
3635 &rdp->expedited_workdone3, s))
3636 return NULL;
3637 return rnp1;
3638}
3639
3640/* Invoked on each online non-idle CPU for expedited quiescent state. */
3641static void sync_sched_exp_handler(void *data)
3642{
3643 struct rcu_data *rdp;
3644 struct rcu_node *rnp;
3645 struct rcu_state *rsp = data;
3646
3647 rdp = this_cpu_ptr(rsp->rda);
3648 rnp = rdp->mynode;
3649 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
3650 __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
3651 return;
3652 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
3653 resched_cpu(smp_processor_id());
3654}
3655
3656/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
3657static void sync_sched_exp_online_cleanup(int cpu)
3658{
3659 struct rcu_data *rdp;
3660 int ret;
3661 struct rcu_node *rnp;
3662 struct rcu_state *rsp = &rcu_sched_state;
3663
3664 rdp = per_cpu_ptr(rsp->rda, cpu);
3665 rnp = rdp->mynode;
3666 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
3667 return;
3668 ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
3669 WARN_ON_ONCE(ret);
3670}
3671
3672/*
3673 * Select the nodes that the upcoming expedited grace period needs
3674 * to wait for.
3675 */
3676static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
3677 smp_call_func_t func)
3678{
3679 int cpu;
3680 unsigned long flags;
3681 unsigned long mask;
3682 unsigned long mask_ofl_test;
3683 unsigned long mask_ofl_ipi;
3684 int ret;
3685 struct rcu_node *rnp;
3686
3687 sync_exp_reset_tree(rsp);
3688 rcu_for_each_leaf_node(rsp, rnp) {
3689 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3690
3691 /* Each pass checks a CPU for identity, offline, and idle. */
3692 mask_ofl_test = 0;
3693 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
3694 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3695 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
3696
3697 if (raw_smp_processor_id() == cpu ||
3698 !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
3699 mask_ofl_test |= rdp->grpmask;
3700 }
3701 mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
3702
3703 /*
3704 * Need to wait for any blocked tasks as well. Note that
3705 * additional blocking tasks will also block the expedited
3706 * GP until such time as the ->expmask bits are cleared.
3707 */
3708 if (rcu_preempt_has_tasks(rnp))
3709 rnp->exp_tasks = rnp->blkd_tasks.next;
3710 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3711
3712 /* IPI the remaining CPUs for expedited quiescent state. */
3713 mask = 1;
3714 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
3715 if (!(mask_ofl_ipi & mask))
3716 continue;
3717retry_ipi:
3718 ret = smp_call_function_single(cpu, func, rsp, 0);
3719 if (!ret) {
3720 mask_ofl_ipi &= ~mask;
3721 continue;
3722 }
3723 /* Failed, raced with offline. */
3724 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3725 if (cpu_online(cpu) &&
3726 (rnp->expmask & mask)) {
3727 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3728 schedule_timeout_uninterruptible(1);
3729 if (cpu_online(cpu) &&
3730 (rnp->expmask & mask))
3731 goto retry_ipi;
3732 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3733 }
3734 if (!(rnp->expmask & mask))
3735 mask_ofl_ipi &= ~mask;
3736 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3737 }
3738 /* Report quiescent states for those that went offline. */
3739 mask_ofl_test |= mask_ofl_ipi;
3740 if (mask_ofl_test)
3741 rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
3742 }
3743}
3744
3745static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
3746{
3747 int cpu;
3748 unsigned long jiffies_stall;
3749 unsigned long jiffies_start;
3750 unsigned long mask;
3751 int ndetected;
3752 struct rcu_node *rnp;
3753 struct rcu_node *rnp_root = rcu_get_root(rsp);
3754 int ret;
3755
3756 jiffies_stall = rcu_jiffies_till_stall_check();
3757 jiffies_start = jiffies;
3758
3759 for (;;) {
3760 ret = swait_event_timeout(
3761 rsp->expedited_wq,
3762 sync_rcu_preempt_exp_done(rnp_root),
3763 jiffies_stall);
3764 if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
3765 return;
3766 if (ret < 0) {
3767 /* Hit a signal, disable CPU stall warnings. */
3768 swait_event(rsp->expedited_wq,
3769 sync_rcu_preempt_exp_done(rnp_root));
3770 return;
3771 }
3772 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
3773 rsp->name);
3774 ndetected = 0;
3775 rcu_for_each_leaf_node(rsp, rnp) {
3776 ndetected = rcu_print_task_exp_stall(rnp);
3777 mask = 1;
3778 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
3779 struct rcu_data *rdp;
3780
3781 if (!(rnp->expmask & mask))
3782 continue;
3783 ndetected++;
3784 rdp = per_cpu_ptr(rsp->rda, cpu);
3785 pr_cont(" %d-%c%c%c", cpu,
3786 "O."[cpu_online(cpu)],
3787 "o."[!!(rdp->grpmask & rnp->expmaskinit)],
3788 "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
3789 }
3790 mask <<= 1;
3791 }
3792 pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
3793 jiffies - jiffies_start, rsp->expedited_sequence,
3794 rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
3795 if (!ndetected) {
3796 pr_err("blocking rcu_node structures:");
3797 rcu_for_each_node_breadth_first(rsp, rnp) {
3798 if (rnp == rnp_root)
3799 continue; /* printed unconditionally */
3800 if (sync_rcu_preempt_exp_done(rnp))
3801 continue;
3802 pr_cont(" l=%u:%d-%d:%#lx/%c",
3803 rnp->level, rnp->grplo, rnp->grphi,
3804 rnp->expmask,
3805 ".T"[!!rnp->exp_tasks]);
3806 }
3807 pr_cont("\n");
3808 }
3809 rcu_for_each_leaf_node(rsp, rnp) {
3810 mask = 1;
3811 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
3812 if (!(rnp->expmask & mask))
3813 continue;
3814 dump_cpu_task(cpu);
3815 }
3816 }
3817 jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
3818 }
3819}
3820
3821/**
3822 * synchronize_sched_expedited - Brute-force RCU-sched grace period
3823 *
3824 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
3825 * approach to force the grace period to end quickly. This consumes
3826 * significant time on all CPUs and is unfriendly to real-time workloads,
3827 * so is thus not recommended for any sort of common-case code. In fact,
3828 * if you are using synchronize_sched_expedited() in a loop, please
3829 * restructure your code to batch your updates, and then use a single
3830 * synchronize_sched() instead.
3831 *
3832 * This implementation can be thought of as an application of sequence
3833 * locking to expedited grace periods, but using the sequence counter to
3834 * determine when someone else has already done the work instead of for
3835 * retrying readers.
3836 */
3837void synchronize_sched_expedited(void)
3838{
3839 unsigned long s;
3840 struct rcu_node *rnp;
3841 struct rcu_state *rsp = &rcu_sched_state;
3842
3843 /* If only one CPU, this is automatically a grace period. */
3844 if (rcu_blocking_is_gp())
3845 return;
3846
3847 /* If expedited grace periods are prohibited, fall back to normal. */
3848 if (rcu_gp_is_normal()) {
3849 wait_rcu_gp(call_rcu_sched);
3850 return;
3851 }
3852
3853 /* Take a snapshot of the sequence number. */
3854 s = rcu_exp_gp_seq_snap(rsp);
3855
3856 rnp = exp_funnel_lock(rsp, s);
3857 if (rnp == NULL)
3858 return; /* Someone else did our work for us. */
3859
3860 rcu_exp_gp_seq_start(rsp);
3861 sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
3862 synchronize_sched_expedited_wait(rsp);
3863
3864 rcu_exp_gp_seq_end(rsp);
3865 mutex_unlock(&rnp->exp_funnel_mutex);
3866}
3867EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
3868
3869/*
3870 * Check to see if there is any immediate RCU-related work to be done
3871 * by the current CPU, for the specified type of RCU, returning 1 if so.
3872 * The checks are in order of increasing expense: checks that can be
3873 * carried out against CPU-local state are performed first. However,
3874 * we must check for CPU stalls first, else we might not get a chance.
3875 */
3876static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
3877{
3878 struct rcu_node *rnp = rdp->mynode;
3879
3880 rdp->n_rcu_pending++;
3881
3882 /* Check for CPU stalls, if enabled. */
3883 check_cpu_stall(rsp, rdp);
3884
3885 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
3886 if (rcu_nohz_full_cpu(rsp))
3887 return 0;
3888
3889 /* Is the RCU core waiting for a quiescent state from this CPU? */
3890 if (rcu_scheduler_fully_active &&
3891 rdp->core_needs_qs && rdp->cpu_no_qs.b.norm &&
3892 rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
3893 rdp->n_rp_core_needs_qs++;
3894 } else if (rdp->core_needs_qs &&
3895 (!rdp->cpu_no_qs.b.norm ||
3896 rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) {
3897 rdp->n_rp_report_qs++;
3898 return 1;
3899 }
3900
3901 /* Does this CPU have callbacks ready to invoke? */
3902 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
3903 rdp->n_rp_cb_ready++;
3904 return 1;
3905 }
3906
3907 /* Has RCU gone idle with this CPU needing another grace period? */
3908 if (cpu_needs_another_gp(rsp, rdp)) {
3909 rdp->n_rp_cpu_needs_gp++;
3910 return 1;
3911 }
3912
3913 /* Has another RCU grace period completed? */
3914 if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
3915 rdp->n_rp_gp_completed++;
3916 return 1;
3917 }
3918
3919 /* Has a new RCU grace period started? */
3920 if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
3921 unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */
3922 rdp->n_rp_gp_started++;
3923 return 1;
3924 }
3925
3926 /* Does this CPU need a deferred NOCB wakeup? */
3927 if (rcu_nocb_need_deferred_wakeup(rdp)) {
3928 rdp->n_rp_nocb_defer_wakeup++;
3929 return 1;
3930 }
3931
3932 /* nothing to do */
3933 rdp->n_rp_need_nothing++;
3934 return 0;
3935}
3936
3937/*
3938 * Check to see if there is any immediate RCU-related work to be done
3939 * by the current CPU, returning 1 if so. This function is part of the
3940 * RCU implementation; it is -not- an exported member of the RCU API.
3941 */
3942static int rcu_pending(void)
3943{
3944 struct rcu_state *rsp;
3945
3946 for_each_rcu_flavor(rsp)
3947 if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3948 return 1;
3949 return 0;
3950}
3951
3952/*
3953 * Return true if the specified CPU has any callback. If all_lazy is
3954 * non-NULL, store an indication of whether all callbacks are lazy.
3955 * (If there are no callbacks, all of them are deemed to be lazy.)
3956 */
3957static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3958{
3959 bool al = true;
3960 bool hc = false;
3961 struct rcu_data *rdp;
3962 struct rcu_state *rsp;
3963
3964 for_each_rcu_flavor(rsp) {
3965 rdp = this_cpu_ptr(rsp->rda);
3966 if (!rdp->nxtlist)
3967 continue;
3968 hc = true;
3969 if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
3970 al = false;
3971 break;
3972 }
3973 }
3974 if (all_lazy)
3975 *all_lazy = al;
3976 return hc;
3977}
3978
3979/*
3980 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
3981 * the compiler is expected to optimize this away.
3982 */
3983static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3984 int cpu, unsigned long done)
3985{
3986 trace_rcu_barrier(rsp->name, s, cpu,
3987 atomic_read(&rsp->barrier_cpu_count), done);
3988}
3989
3990/*
3991 * RCU callback function for _rcu_barrier(). If we are last, wake
3992 * up the task executing _rcu_barrier().
3993 */
3994static void rcu_barrier_callback(struct rcu_head *rhp)
3995{
3996 struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
3997 struct rcu_state *rsp = rdp->rsp;
3998
3999 if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
4000 _rcu_barrier_trace(rsp, "LastCB", -1, rsp->barrier_sequence);
4001 complete(&rsp->barrier_completion);
4002 } else {
4003 _rcu_barrier_trace(rsp, "CB", -1, rsp->barrier_sequence);
4004 }
4005}
4006
4007/*
4008 * Called with preemption disabled, and from cross-cpu IRQ context.
4009 */
4010static void rcu_barrier_func(void *type)
4011{
4012 struct rcu_state *rsp = type;
4013 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
4014
4015 _rcu_barrier_trace(rsp, "IRQ", -1, rsp->barrier_sequence);
4016 atomic_inc(&rsp->barrier_cpu_count);
4017 rsp->call(&rdp->barrier_head, rcu_barrier_callback);
4018}
4019
4020/*
4021 * Orchestrate the specified type of RCU barrier, waiting for all
4022 * RCU callbacks of the specified type to complete.
4023 */
4024static void _rcu_barrier(struct rcu_state *rsp)
4025{
4026 int cpu;
4027 struct rcu_data *rdp;
4028 unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);
4029
4030 _rcu_barrier_trace(rsp, "Begin", -1, s);
4031
4032 /* Take mutex to serialize concurrent rcu_barrier() requests. */
4033 mutex_lock(&rsp->barrier_mutex);
4034
4035 /* Did someone else do our work for us? */
4036 if (rcu_seq_done(&rsp->barrier_sequence, s)) {
4037 _rcu_barrier_trace(rsp, "EarlyExit", -1, rsp->barrier_sequence);
4038 smp_mb(); /* caller's subsequent code after above check. */
4039 mutex_unlock(&rsp->barrier_mutex);
4040 return;
4041 }
4042
4043 /* Mark the start of the barrier operation. */
4044 rcu_seq_start(&rsp->barrier_sequence);
4045 _rcu_barrier_trace(rsp, "Inc1", -1, rsp->barrier_sequence);
4046
4047 /*
4048 * Initialize the count to one rather than to zero in order to
4049 * avoid a too-soon return to zero in case of a short grace period
4050 * (or preemption of this task). Exclude CPU-hotplug operations
4051 * to ensure that no offline CPU has callbacks queued.
4052 */
4053 init_completion(&rsp->barrier_completion);
4054 atomic_set(&rsp->barrier_cpu_count, 1);
4055 get_online_cpus();
4056
4057 /*
4058 * Force each CPU with callbacks to register a new callback.
4059 * When that callback is invoked, we will know that all of the
4060 * corresponding CPU's preceding callbacks have been invoked.
4061 */
4062 for_each_possible_cpu(cpu) {
4063 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
4064 continue;
4065 rdp = per_cpu_ptr(rsp->rda, cpu);
4066 if (rcu_is_nocb_cpu(cpu)) {
4067 if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
4068 _rcu_barrier_trace(rsp, "OfflineNoCB", cpu,
4069 rsp->barrier_sequence);
4070 } else {
4071 _rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
4072 rsp->barrier_sequence);
4073 smp_mb__before_atomic();
4074 atomic_inc(&rsp->barrier_cpu_count);
4075 __call_rcu(&rdp->barrier_head,
4076 rcu_barrier_callback, rsp, cpu, 0);
4077 }
4078 } else if (READ_ONCE(rdp->qlen)) {
4079 _rcu_barrier_trace(rsp, "OnlineQ", cpu,
4080 rsp->barrier_sequence);
4081 smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
4082 } else {
4083 _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
4084 rsp->barrier_sequence);
4085 }
4086 }
4087 put_online_cpus();
4088
4089 /*
4090 * Now that we have an rcu_barrier_callback() callback on each
4091 * CPU, and thus each counted, remove the initial count.
4092 */
4093 if (atomic_dec_and_test(&rsp->barrier_cpu_count))
4094 complete(&rsp->barrier_completion);
4095
4096 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
4097 wait_for_completion(&rsp->barrier_completion);
4098
4099 /* Mark the end of the barrier operation. */
4100 _rcu_barrier_trace(rsp, "Inc2", -1, rsp->barrier_sequence);
4101 rcu_seq_end(&rsp->barrier_sequence);
4102
4103 /* Other rcu_barrier() invocations can now safely proceed. */
4104 mutex_unlock(&rsp->barrier_mutex);
4105}
4106
4107/**
4108 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
4109 */
4110void rcu_barrier_bh(void)
4111{
4112 _rcu_barrier(&rcu_bh_state);
4113}
4114EXPORT_SYMBOL_GPL(rcu_barrier_bh);
4115
4116/**
4117 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
4118 */
4119void rcu_barrier_sched(void)
4120{
4121 _rcu_barrier(&rcu_sched_state);
4122}
4123EXPORT_SYMBOL_GPL(rcu_barrier_sched);
4124
4125/*
4126 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
4127 * first CPU in a given leaf rcu_node structure coming online. The caller
4128 * must hold the corresponding leaf rcu_node ->lock with interrrupts
4129 * disabled.
4130 */
4131static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
4132{
4133 long mask;
4134 struct rcu_node *rnp = rnp_leaf;
4135
4136 for (;;) {
4137 mask = rnp->grpmask;
4138 rnp = rnp->parent;
4139 if (rnp == NULL)
4140 return;
4141 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
4142 rnp->qsmaskinit |= mask;
4143 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
4144 }
4145}
4146
4147/*
4148 * Do boot-time initialization of a CPU's per-CPU RCU data.
4149 */
4150static void __init
4151rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
4152{
4153 unsigned long flags;
4154 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
4155 struct rcu_node *rnp = rcu_get_root(rsp);
4156
4157 /* Set up local state, ensuring consistent view of global state. */
4158 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4159 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
4160 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
4161 WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
4162 WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
4163 rdp->cpu = cpu;
4164 rdp->rsp = rsp;
4165 mutex_init(&rdp->exp_funnel_mutex);
4166 rcu_boot_init_nocb_percpu_data(rdp);
4167 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4168}
4169
4170/*
4171 * Initialize a CPU's per-CPU RCU data. Note that only one online or
4172 * offline event can be happening at a given time. Note also that we
4173 * can accept some slop in the rsp->completed access due to the fact
4174 * that this CPU cannot possibly have any RCU callbacks in flight yet.
4175 */
4176static void
4177rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
4178{
4179 unsigned long flags;
4180 unsigned long mask;
4181 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
4182 struct rcu_node *rnp = rcu_get_root(rsp);
4183
4184 /* Set up local state, ensuring consistent view of global state. */
4185 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4186 rdp->qlen_last_fqs_check = 0;
4187 rdp->n_force_qs_snap = rsp->n_force_qs;
4188 rdp->blimit = blimit;
4189 if (!rdp->nxtlist)
4190 init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
4191 rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
4192 rcu_sysidle_init_percpu_data(rdp->dynticks);
4193 atomic_set(&rdp->dynticks->dynticks,
4194 (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
4195 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
4196
4197 /*
4198 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
4199 * propagation up the rcu_node tree will happen at the beginning
4200 * of the next grace period.
4201 */
4202 rnp = rdp->mynode;
4203 mask = rdp->grpmask;
4204 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
4205 rnp->qsmaskinitnext |= mask;
4206 rnp->expmaskinitnext |= mask;
4207 if (!rdp->beenonline)
4208 WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1);
4209 rdp->beenonline = true; /* We have now been online. */
4210 rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
4211 rdp->completed = rnp->completed;
4212 rdp->cpu_no_qs.b.norm = true;
4213 rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu);
4214 rdp->core_needs_qs = false;
4215 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
4216 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4217}
4218
4219static void rcu_prepare_cpu(int cpu)
4220{
4221 struct rcu_state *rsp;
4222
4223 for_each_rcu_flavor(rsp)
4224 rcu_init_percpu_data(cpu, rsp);
4225}
4226
4227#ifdef CONFIG_HOTPLUG_CPU
4228/*
4229 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
4230 * function. We now remove it from the rcu_node tree's ->qsmaskinit
4231 * bit masks.
4232 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
4233 * function. We now remove it from the rcu_node tree's ->qsmaskinit
4234 * bit masks.
4235 */
4236static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
4237{
4238 unsigned long flags;
4239 unsigned long mask;
4240 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
4241 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
4242
4243 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
4244 return;
4245
4246 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
4247 mask = rdp->grpmask;
4248 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
4249 rnp->qsmaskinitnext &= ~mask;
4250 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4251}
4252
4253void rcu_report_dead(unsigned int cpu)
4254{
4255 struct rcu_state *rsp;
4256
4257 /* QS for any half-done expedited RCU-sched GP. */
4258 preempt_disable();
4259 rcu_report_exp_rdp(&rcu_sched_state,
4260 this_cpu_ptr(rcu_sched_state.rda), true);
4261 preempt_enable();
4262 for_each_rcu_flavor(rsp)
4263 rcu_cleanup_dying_idle_cpu(cpu, rsp);
4264}
4265#endif
4266
4267/*
4268 * Handle CPU online/offline notification events.
4269 */
4270int rcu_cpu_notify(struct notifier_block *self,
4271 unsigned long action, void *hcpu)
4272{
4273 long cpu = (long)hcpu;
4274 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
4275 struct rcu_node *rnp = rdp->mynode;
4276 struct rcu_state *rsp;
4277
4278 switch (action) {
4279 case CPU_UP_PREPARE:
4280 case CPU_UP_PREPARE_FROZEN:
4281 rcu_prepare_cpu(cpu);
4282 rcu_prepare_kthreads(cpu);
4283 rcu_spawn_all_nocb_kthreads(cpu);
4284 break;
4285 case CPU_ONLINE:
4286 case CPU_DOWN_FAILED:
4287 sync_sched_exp_online_cleanup(cpu);
4288 rcu_boost_kthread_setaffinity(rnp, -1);
4289 break;
4290 case CPU_DOWN_PREPARE:
4291 rcu_boost_kthread_setaffinity(rnp, cpu);
4292 break;
4293 case CPU_DYING:
4294 case CPU_DYING_FROZEN:
4295 for_each_rcu_flavor(rsp)
4296 rcu_cleanup_dying_cpu(rsp);
4297 break;
4298 case CPU_DEAD:
4299 case CPU_DEAD_FROZEN:
4300 case CPU_UP_CANCELED:
4301 case CPU_UP_CANCELED_FROZEN:
4302 for_each_rcu_flavor(rsp) {
4303 rcu_cleanup_dead_cpu(cpu, rsp);
4304 do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
4305 }
4306 break;
4307 default:
4308 break;
4309 }
4310 return NOTIFY_OK;
4311}
4312
4313static int rcu_pm_notify(struct notifier_block *self,
4314 unsigned long action, void *hcpu)
4315{
4316 switch (action) {
4317 case PM_HIBERNATION_PREPARE:
4318 case PM_SUSPEND_PREPARE:
4319 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
4320 rcu_expedite_gp();
4321 break;
4322 case PM_POST_HIBERNATION:
4323 case PM_POST_SUSPEND:
4324 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
4325 rcu_unexpedite_gp();
4326 break;
4327 default:
4328 break;
4329 }
4330 return NOTIFY_OK;
4331}
4332
4333/*
4334 * Spawn the kthreads that handle each RCU flavor's grace periods.
4335 */
4336static int __init rcu_spawn_gp_kthread(void)
4337{
4338 unsigned long flags;
4339 int kthread_prio_in = kthread_prio;
4340 struct rcu_node *rnp;
4341 struct rcu_state *rsp;
4342 struct sched_param sp;
4343 struct task_struct *t;
4344
4345 /* Force priority into range. */
4346 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
4347 kthread_prio = 1;
4348 else if (kthread_prio < 0)
4349 kthread_prio = 0;
4350 else if (kthread_prio > 99)
4351 kthread_prio = 99;
4352 if (kthread_prio != kthread_prio_in)
4353 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
4354 kthread_prio, kthread_prio_in);
4355
4356 rcu_scheduler_fully_active = 1;
4357 for_each_rcu_flavor(rsp) {
4358 t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
4359 BUG_ON(IS_ERR(t));
4360 rnp = rcu_get_root(rsp);
4361 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4362 rsp->gp_kthread = t;
4363 if (kthread_prio) {
4364 sp.sched_priority = kthread_prio;
4365 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
4366 }
4367 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4368 wake_up_process(t);
4369 }
4370 rcu_spawn_nocb_kthreads();
4371 rcu_spawn_boost_kthreads();
4372 return 0;
4373}
4374early_initcall(rcu_spawn_gp_kthread);
4375
4376/*
4377 * This function is invoked towards the end of the scheduler's initialization
4378 * process. Before this is called, the idle task might contain
4379 * RCU read-side critical sections (during which time, this idle
4380 * task is booting the system). After this function is called, the
4381 * idle tasks are prohibited from containing RCU read-side critical
4382 * sections. This function also enables RCU lockdep checking.
4383 */
4384void rcu_scheduler_starting(void)
4385{
4386 WARN_ON(num_online_cpus() != 1);
4387 WARN_ON(nr_context_switches() > 0);
4388 rcu_scheduler_active = 1;
4389}
4390
4391/*
4392 * Compute the per-level fanout, either using the exact fanout specified
4393 * or balancing the tree, depending on the rcu_fanout_exact boot parameter.
4394 */
4395static void __init rcu_init_levelspread(int *levelspread, const int *levelcnt)
4396{
4397 int i;
4398
4399 if (rcu_fanout_exact) {
4400 levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
4401 for (i = rcu_num_lvls - 2; i >= 0; i--)
4402 levelspread[i] = RCU_FANOUT;
4403 } else {
4404 int ccur;
4405 int cprv;
4406
4407 cprv = nr_cpu_ids;
4408 for (i = rcu_num_lvls - 1; i >= 0; i--) {
4409 ccur = levelcnt[i];
4410 levelspread[i] = (cprv + ccur - 1) / ccur;
4411 cprv = ccur;
4412 }
4413 }
4414}
4415
4416/*
4417 * Helper function for rcu_init() that initializes one rcu_state structure.
4418 */
4419static void __init rcu_init_one(struct rcu_state *rsp)
4420{
4421 static const char * const buf[] = RCU_NODE_NAME_INIT;
4422 static const char * const fqs[] = RCU_FQS_NAME_INIT;
4423 static const char * const exp[] = RCU_EXP_NAME_INIT;
4424 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
4425 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
4426 static struct lock_class_key rcu_exp_class[RCU_NUM_LVLS];
4427 static u8 fl_mask = 0x1;
4428
4429 int levelcnt[RCU_NUM_LVLS]; /* # nodes in each level. */
4430 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
4431 int cpustride = 1;
4432 int i;
4433 int j;
4434 struct rcu_node *rnp;
4435
4436 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
4437
4438 /* Silence gcc 4.8 false positive about array index out of range. */
4439 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
4440 panic("rcu_init_one: rcu_num_lvls out of range");
4441
4442 /* Initialize the level-tracking arrays. */
4443
4444 for (i = 0; i < rcu_num_lvls; i++)
4445 levelcnt[i] = num_rcu_lvl[i];
4446 for (i = 1; i < rcu_num_lvls; i++)
4447 rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];
4448 rcu_init_levelspread(levelspread, levelcnt);
4449 rsp->flavor_mask = fl_mask;
4450 fl_mask <<= 1;
4451
4452 /* Initialize the elements themselves, starting from the leaves. */
4453
4454 for (i = rcu_num_lvls - 1; i >= 0; i--) {
4455 cpustride *= levelspread[i];
4456 rnp = rsp->level[i];
4457 for (j = 0; j < levelcnt[i]; j++, rnp++) {
4458 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
4459 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
4460 &rcu_node_class[i], buf[i]);
4461 raw_spin_lock_init(&rnp->fqslock);
4462 lockdep_set_class_and_name(&rnp->fqslock,
4463 &rcu_fqs_class[i], fqs[i]);
4464 rnp->gpnum = rsp->gpnum;
4465 rnp->completed = rsp->completed;
4466 rnp->qsmask = 0;
4467 rnp->qsmaskinit = 0;
4468 rnp->grplo = j * cpustride;
4469 rnp->grphi = (j + 1) * cpustride - 1;
4470 if (rnp->grphi >= nr_cpu_ids)
4471 rnp->grphi = nr_cpu_ids - 1;
4472 if (i == 0) {
4473 rnp->grpnum = 0;
4474 rnp->grpmask = 0;
4475 rnp->parent = NULL;
4476 } else {
4477 rnp->grpnum = j % levelspread[i - 1];
4478 rnp->grpmask = 1UL << rnp->grpnum;
4479 rnp->parent = rsp->level[i - 1] +
4480 j / levelspread[i - 1];
4481 }
4482 rnp->level = i;
4483 INIT_LIST_HEAD(&rnp->blkd_tasks);
4484 rcu_init_one_nocb(rnp);
4485 mutex_init(&rnp->exp_funnel_mutex);
4486 lockdep_set_class_and_name(&rnp->exp_funnel_mutex,
4487 &rcu_exp_class[i], exp[i]);
4488 }
4489 }
4490
4491 init_swait_queue_head(&rsp->gp_wq);
4492 init_swait_queue_head(&rsp->expedited_wq);
4493 rnp = rsp->level[rcu_num_lvls - 1];
4494 for_each_possible_cpu(i) {
4495 while (i > rnp->grphi)
4496 rnp++;
4497 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
4498 rcu_boot_init_percpu_data(i, rsp);
4499 }
4500 list_add(&rsp->flavors, &rcu_struct_flavors);
4501}
4502
4503/*
4504 * Compute the rcu_node tree geometry from kernel parameters. This cannot
4505 * replace the definitions in tree.h because those are needed to size
4506 * the ->node array in the rcu_state structure.
4507 */
4508static void __init rcu_init_geometry(void)
4509{
4510 ulong d;
4511 int i;
4512 int rcu_capacity[RCU_NUM_LVLS];
4513
4514 /*
4515 * Initialize any unspecified boot parameters.
4516 * The default values of jiffies_till_first_fqs and
4517 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
4518 * value, which is a function of HZ, then adding one for each
4519 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
4520 */
4521 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
4522 if (jiffies_till_first_fqs == ULONG_MAX)
4523 jiffies_till_first_fqs = d;
4524 if (jiffies_till_next_fqs == ULONG_MAX)
4525 jiffies_till_next_fqs = d;
4526
4527 /* If the compile-time values are accurate, just leave. */
4528 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
4529 nr_cpu_ids == NR_CPUS)
4530 return;
4531 pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
4532 rcu_fanout_leaf, nr_cpu_ids);
4533
4534 /*
4535 * The boot-time rcu_fanout_leaf parameter must be at least two
4536 * and cannot exceed the number of bits in the rcu_node masks.
4537 * Complain and fall back to the compile-time values if this
4538 * limit is exceeded.
4539 */
4540 if (rcu_fanout_leaf < 2 ||
4541 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
4542 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4543 WARN_ON(1);
4544 return;
4545 }
4546
4547 /*
4548 * Compute number of nodes that can be handled an rcu_node tree
4549 * with the given number of levels.
4550 */
4551 rcu_capacity[0] = rcu_fanout_leaf;
4552 for (i = 1; i < RCU_NUM_LVLS; i++)
4553 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
4554
4555 /*
4556 * The tree must be able to accommodate the configured number of CPUs.
4557 * If this limit is exceeded, fall back to the compile-time values.
4558 */
4559 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
4560 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4561 WARN_ON(1);
4562 return;
4563 }
4564
4565 /* Calculate the number of levels in the tree. */
4566 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
4567 }
4568 rcu_num_lvls = i + 1;
4569
4570 /* Calculate the number of rcu_nodes at each level of the tree. */
4571 for (i = 0; i < rcu_num_lvls; i++) {
4572 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
4573 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
4574 }
4575
4576 /* Calculate the total number of rcu_node structures. */
4577 rcu_num_nodes = 0;
4578 for (i = 0; i < rcu_num_lvls; i++)
4579 rcu_num_nodes += num_rcu_lvl[i];
4580}
4581
4582/*
4583 * Dump out the structure of the rcu_node combining tree associated
4584 * with the rcu_state structure referenced by rsp.
4585 */
4586static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
4587{
4588 int level = 0;
4589 struct rcu_node *rnp;
4590
4591 pr_info("rcu_node tree layout dump\n");
4592 pr_info(" ");
4593 rcu_for_each_node_breadth_first(rsp, rnp) {
4594 if (rnp->level != level) {
4595 pr_cont("\n");
4596 pr_info(" ");
4597 level = rnp->level;
4598 }
4599 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
4600 }
4601 pr_cont("\n");
4602}
4603
4604void __init rcu_init(void)
4605{
4606 int cpu;
4607
4608 rcu_early_boot_tests();
4609
4610 rcu_bootup_announce();
4611 rcu_init_geometry();
4612 rcu_init_one(&rcu_bh_state);
4613 rcu_init_one(&rcu_sched_state);
4614 if (dump_tree)
4615 rcu_dump_rcu_node_tree(&rcu_sched_state);
4616 __rcu_init_preempt();
4617 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
4618
4619 /*
4620 * We don't need protection against CPU-hotplug here because
4621 * this is called early in boot, before either interrupts
4622 * or the scheduler are operational.
4623 */
4624 cpu_notifier(rcu_cpu_notify, 0);
4625 pm_notifier(rcu_pm_notify, 0);
4626 for_each_online_cpu(cpu)
4627 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
4628}
4629
4630#include "tree_plugin.h"
1/*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright IBM Corporation, 2008
19 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
23 *
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 *
27 * For detailed explanation of Read-Copy Update mechanism see -
28 * Documentation/RCU
29 */
30#include <linux/types.h>
31#include <linux/kernel.h>
32#include <linux/init.h>
33#include <linux/spinlock.h>
34#include <linux/smp.h>
35#include <linux/rcupdate.h>
36#include <linux/interrupt.h>
37#include <linux/sched.h>
38#include <linux/nmi.h>
39#include <linux/atomic.h>
40#include <linux/bitops.h>
41#include <linux/export.h>
42#include <linux/completion.h>
43#include <linux/moduleparam.h>
44#include <linux/module.h>
45#include <linux/percpu.h>
46#include <linux/notifier.h>
47#include <linux/cpu.h>
48#include <linux/mutex.h>
49#include <linux/time.h>
50#include <linux/kernel_stat.h>
51#include <linux/wait.h>
52#include <linux/kthread.h>
53#include <linux/prefetch.h>
54#include <linux/delay.h>
55#include <linux/stop_machine.h>
56#include <linux/random.h>
57#include <linux/ftrace_event.h>
58#include <linux/suspend.h>
59
60#include "tree.h"
61#include "rcu.h"
62
63MODULE_ALIAS("rcutree");
64#ifdef MODULE_PARAM_PREFIX
65#undef MODULE_PARAM_PREFIX
66#endif
67#define MODULE_PARAM_PREFIX "rcutree."
68
69/* Data structures. */
70
71static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
72static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
73
74/*
75 * In order to export the rcu_state name to the tracing tools, it
76 * needs to be added in the __tracepoint_string section.
77 * This requires defining a separate variable tp_<sname>_varname
78 * that points to the string being used, and this will allow
79 * the tracing userspace tools to be able to decipher the string
80 * address to the matching string.
81 */
82#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
83static char sname##_varname[] = #sname; \
84static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
85struct rcu_state sname##_state = { \
86 .level = { &sname##_state.node[0] }, \
87 .call = cr, \
88 .fqs_state = RCU_GP_IDLE, \
89 .gpnum = 0UL - 300UL, \
90 .completed = 0UL - 300UL, \
91 .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
92 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
93 .orphan_donetail = &sname##_state.orphan_donelist, \
94 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
95 .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
96 .name = sname##_varname, \
97 .abbr = sabbr, \
98}; \
99DEFINE_PER_CPU(struct rcu_data, sname##_data)
100
101RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
102RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
103
104static struct rcu_state *rcu_state;
105LIST_HEAD(rcu_struct_flavors);
106
107/* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
108static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
109module_param(rcu_fanout_leaf, int, 0444);
110int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
111static int num_rcu_lvl[] = { /* Number of rcu_nodes at specified level. */
112 NUM_RCU_LVL_0,
113 NUM_RCU_LVL_1,
114 NUM_RCU_LVL_2,
115 NUM_RCU_LVL_3,
116 NUM_RCU_LVL_4,
117};
118int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
119
120/*
121 * The rcu_scheduler_active variable transitions from zero to one just
122 * before the first task is spawned. So when this variable is zero, RCU
123 * can assume that there is but one task, allowing RCU to (for example)
124 * optimize synchronize_sched() to a simple barrier(). When this variable
125 * is one, RCU must actually do all the hard work required to detect real
126 * grace periods. This variable is also used to suppress boot-time false
127 * positives from lockdep-RCU error checking.
128 */
129int rcu_scheduler_active __read_mostly;
130EXPORT_SYMBOL_GPL(rcu_scheduler_active);
131
132/*
133 * The rcu_scheduler_fully_active variable transitions from zero to one
134 * during the early_initcall() processing, which is after the scheduler
135 * is capable of creating new tasks. So RCU processing (for example,
136 * creating tasks for RCU priority boosting) must be delayed until after
137 * rcu_scheduler_fully_active transitions from zero to one. We also
138 * currently delay invocation of any RCU callbacks until after this point.
139 *
140 * It might later prove better for people registering RCU callbacks during
141 * early boot to take responsibility for these callbacks, but one step at
142 * a time.
143 */
144static int rcu_scheduler_fully_active __read_mostly;
145
146#ifdef CONFIG_RCU_BOOST
147
148/*
149 * Control variables for per-CPU and per-rcu_node kthreads. These
150 * handle all flavors of RCU.
151 */
152static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
153DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
154DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
155DEFINE_PER_CPU(char, rcu_cpu_has_work);
156
157#endif /* #ifdef CONFIG_RCU_BOOST */
158
159static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
160static void invoke_rcu_core(void);
161static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
162
163/*
164 * Track the rcutorture test sequence number and the update version
165 * number within a given test. The rcutorture_testseq is incremented
166 * on every rcutorture module load and unload, so has an odd value
167 * when a test is running. The rcutorture_vernum is set to zero
168 * when rcutorture starts and is incremented on each rcutorture update.
169 * These variables enable correlating rcutorture output with the
170 * RCU tracing information.
171 */
172unsigned long rcutorture_testseq;
173unsigned long rcutorture_vernum;
174
175/*
176 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
177 * permit this function to be invoked without holding the root rcu_node
178 * structure's ->lock, but of course results can be subject to change.
179 */
180static int rcu_gp_in_progress(struct rcu_state *rsp)
181{
182 return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
183}
184
185/*
186 * Note a quiescent state. Because we do not need to know
187 * how many quiescent states passed, just if there was at least
188 * one since the start of the grace period, this just sets a flag.
189 * The caller must have disabled preemption.
190 */
191void rcu_sched_qs(int cpu)
192{
193 struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
194
195 if (rdp->passed_quiesce == 0)
196 trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("cpuqs"));
197 rdp->passed_quiesce = 1;
198}
199
200void rcu_bh_qs(int cpu)
201{
202 struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
203
204 if (rdp->passed_quiesce == 0)
205 trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("cpuqs"));
206 rdp->passed_quiesce = 1;
207}
208
209/*
210 * Note a context switch. This is a quiescent state for RCU-sched,
211 * and requires special handling for preemptible RCU.
212 * The caller must have disabled preemption.
213 */
214void rcu_note_context_switch(int cpu)
215{
216 trace_rcu_utilization(TPS("Start context switch"));
217 rcu_sched_qs(cpu);
218 rcu_preempt_note_context_switch(cpu);
219 trace_rcu_utilization(TPS("End context switch"));
220}
221EXPORT_SYMBOL_GPL(rcu_note_context_switch);
222
223static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
224 .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
225 .dynticks = ATOMIC_INIT(1),
226#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
227 .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
228 .dynticks_idle = ATOMIC_INIT(1),
229#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
230};
231
232static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */
233static long qhimark = 10000; /* If this many pending, ignore blimit. */
234static long qlowmark = 100; /* Once only this many pending, use blimit. */
235
236module_param(blimit, long, 0444);
237module_param(qhimark, long, 0444);
238module_param(qlowmark, long, 0444);
239
240static ulong jiffies_till_first_fqs = ULONG_MAX;
241static ulong jiffies_till_next_fqs = ULONG_MAX;
242
243module_param(jiffies_till_first_fqs, ulong, 0644);
244module_param(jiffies_till_next_fqs, ulong, 0644);
245
246static void rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
247 struct rcu_data *rdp);
248static void force_qs_rnp(struct rcu_state *rsp,
249 int (*f)(struct rcu_data *rsp, bool *isidle,
250 unsigned long *maxj),
251 bool *isidle, unsigned long *maxj);
252static void force_quiescent_state(struct rcu_state *rsp);
253static int rcu_pending(int cpu);
254
255/*
256 * Return the number of RCU-sched batches processed thus far for debug & stats.
257 */
258long rcu_batches_completed_sched(void)
259{
260 return rcu_sched_state.completed;
261}
262EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
263
264/*
265 * Return the number of RCU BH batches processed thus far for debug & stats.
266 */
267long rcu_batches_completed_bh(void)
268{
269 return rcu_bh_state.completed;
270}
271EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
272
273/*
274 * Force a quiescent state for RCU BH.
275 */
276void rcu_bh_force_quiescent_state(void)
277{
278 force_quiescent_state(&rcu_bh_state);
279}
280EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
281
282/*
283 * Record the number of times rcutorture tests have been initiated and
284 * terminated. This information allows the debugfs tracing stats to be
285 * correlated to the rcutorture messages, even when the rcutorture module
286 * is being repeatedly loaded and unloaded. In other words, we cannot
287 * store this state in rcutorture itself.
288 */
289void rcutorture_record_test_transition(void)
290{
291 rcutorture_testseq++;
292 rcutorture_vernum = 0;
293}
294EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
295
296/*
297 * Record the number of writer passes through the current rcutorture test.
298 * This is also used to correlate debugfs tracing stats with the rcutorture
299 * messages.
300 */
301void rcutorture_record_progress(unsigned long vernum)
302{
303 rcutorture_vernum++;
304}
305EXPORT_SYMBOL_GPL(rcutorture_record_progress);
306
307/*
308 * Force a quiescent state for RCU-sched.
309 */
310void rcu_sched_force_quiescent_state(void)
311{
312 force_quiescent_state(&rcu_sched_state);
313}
314EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
315
316/*
317 * Does the CPU have callbacks ready to be invoked?
318 */
319static int
320cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
321{
322 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
323 rdp->nxttail[RCU_DONE_TAIL] != NULL;
324}
325
326/*
327 * Does the current CPU require a not-yet-started grace period?
328 * The caller must have disabled interrupts to prevent races with
329 * normal callback registry.
330 */
331static int
332cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
333{
334 int i;
335
336 if (rcu_gp_in_progress(rsp))
337 return 0; /* No, a grace period is already in progress. */
338 if (rcu_nocb_needs_gp(rsp))
339 return 1; /* Yes, a no-CBs CPU needs one. */
340 if (!rdp->nxttail[RCU_NEXT_TAIL])
341 return 0; /* No, this is a no-CBs (or offline) CPU. */
342 if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
343 return 1; /* Yes, this CPU has newly registered callbacks. */
344 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
345 if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
346 ULONG_CMP_LT(ACCESS_ONCE(rsp->completed),
347 rdp->nxtcompleted[i]))
348 return 1; /* Yes, CBs for future grace period. */
349 return 0; /* No grace period needed. */
350}
351
352/*
353 * Return the root node of the specified rcu_state structure.
354 */
355static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
356{
357 return &rsp->node[0];
358}
359
360/*
361 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
362 *
363 * If the new value of the ->dynticks_nesting counter now is zero,
364 * we really have entered idle, and must do the appropriate accounting.
365 * The caller must have disabled interrupts.
366 */
367static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
368 bool user)
369{
370 struct rcu_state *rsp;
371 struct rcu_data *rdp;
372
373 trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
374 if (!user && !is_idle_task(current)) {
375 struct task_struct *idle __maybe_unused =
376 idle_task(smp_processor_id());
377
378 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
379 ftrace_dump(DUMP_ORIG);
380 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
381 current->pid, current->comm,
382 idle->pid, idle->comm); /* must be idle task! */
383 }
384 for_each_rcu_flavor(rsp) {
385 rdp = this_cpu_ptr(rsp->rda);
386 do_nocb_deferred_wakeup(rdp);
387 }
388 rcu_prepare_for_idle(smp_processor_id());
389 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
390 smp_mb__before_atomic_inc(); /* See above. */
391 atomic_inc(&rdtp->dynticks);
392 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
393 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
394
395 /*
396 * It is illegal to enter an extended quiescent state while
397 * in an RCU read-side critical section.
398 */
399 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
400 "Illegal idle entry in RCU read-side critical section.");
401 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
402 "Illegal idle entry in RCU-bh read-side critical section.");
403 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
404 "Illegal idle entry in RCU-sched read-side critical section.");
405}
406
407/*
408 * Enter an RCU extended quiescent state, which can be either the
409 * idle loop or adaptive-tickless usermode execution.
410 */
411static void rcu_eqs_enter(bool user)
412{
413 long long oldval;
414 struct rcu_dynticks *rdtp;
415
416 rdtp = this_cpu_ptr(&rcu_dynticks);
417 oldval = rdtp->dynticks_nesting;
418 WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
419 if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
420 rdtp->dynticks_nesting = 0;
421 rcu_eqs_enter_common(rdtp, oldval, user);
422 } else {
423 rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
424 }
425}
426
427/**
428 * rcu_idle_enter - inform RCU that current CPU is entering idle
429 *
430 * Enter idle mode, in other words, -leave- the mode in which RCU
431 * read-side critical sections can occur. (Though RCU read-side
432 * critical sections can occur in irq handlers in idle, a possibility
433 * handled by irq_enter() and irq_exit().)
434 *
435 * We crowbar the ->dynticks_nesting field to zero to allow for
436 * the possibility of usermode upcalls having messed up our count
437 * of interrupt nesting level during the prior busy period.
438 */
439void rcu_idle_enter(void)
440{
441 unsigned long flags;
442
443 local_irq_save(flags);
444 rcu_eqs_enter(false);
445 rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks), 0);
446 local_irq_restore(flags);
447}
448EXPORT_SYMBOL_GPL(rcu_idle_enter);
449
450#ifdef CONFIG_RCU_USER_QS
451/**
452 * rcu_user_enter - inform RCU that we are resuming userspace.
453 *
454 * Enter RCU idle mode right before resuming userspace. No use of RCU
455 * is permitted between this call and rcu_user_exit(). This way the
456 * CPU doesn't need to maintain the tick for RCU maintenance purposes
457 * when the CPU runs in userspace.
458 */
459void rcu_user_enter(void)
460{
461 rcu_eqs_enter(1);
462}
463#endif /* CONFIG_RCU_USER_QS */
464
465/**
466 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
467 *
468 * Exit from an interrupt handler, which might possibly result in entering
469 * idle mode, in other words, leaving the mode in which read-side critical
470 * sections can occur.
471 *
472 * This code assumes that the idle loop never does anything that might
473 * result in unbalanced calls to irq_enter() and irq_exit(). If your
474 * architecture violates this assumption, RCU will give you what you
475 * deserve, good and hard. But very infrequently and irreproducibly.
476 *
477 * Use things like work queues to work around this limitation.
478 *
479 * You have been warned.
480 */
481void rcu_irq_exit(void)
482{
483 unsigned long flags;
484 long long oldval;
485 struct rcu_dynticks *rdtp;
486
487 local_irq_save(flags);
488 rdtp = this_cpu_ptr(&rcu_dynticks);
489 oldval = rdtp->dynticks_nesting;
490 rdtp->dynticks_nesting--;
491 WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
492 if (rdtp->dynticks_nesting)
493 trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
494 else
495 rcu_eqs_enter_common(rdtp, oldval, true);
496 rcu_sysidle_enter(rdtp, 1);
497 local_irq_restore(flags);
498}
499
500/*
501 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
502 *
503 * If the new value of the ->dynticks_nesting counter was previously zero,
504 * we really have exited idle, and must do the appropriate accounting.
505 * The caller must have disabled interrupts.
506 */
507static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
508 int user)
509{
510 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
511 atomic_inc(&rdtp->dynticks);
512 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
513 smp_mb__after_atomic_inc(); /* See above. */
514 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
515 rcu_cleanup_after_idle(smp_processor_id());
516 trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
517 if (!user && !is_idle_task(current)) {
518 struct task_struct *idle __maybe_unused =
519 idle_task(smp_processor_id());
520
521 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
522 oldval, rdtp->dynticks_nesting);
523 ftrace_dump(DUMP_ORIG);
524 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
525 current->pid, current->comm,
526 idle->pid, idle->comm); /* must be idle task! */
527 }
528}
529
530/*
531 * Exit an RCU extended quiescent state, which can be either the
532 * idle loop or adaptive-tickless usermode execution.
533 */
534static void rcu_eqs_exit(bool user)
535{
536 struct rcu_dynticks *rdtp;
537 long long oldval;
538
539 rdtp = this_cpu_ptr(&rcu_dynticks);
540 oldval = rdtp->dynticks_nesting;
541 WARN_ON_ONCE(oldval < 0);
542 if (oldval & DYNTICK_TASK_NEST_MASK) {
543 rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
544 } else {
545 rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
546 rcu_eqs_exit_common(rdtp, oldval, user);
547 }
548}
549
550/**
551 * rcu_idle_exit - inform RCU that current CPU is leaving idle
552 *
553 * Exit idle mode, in other words, -enter- the mode in which RCU
554 * read-side critical sections can occur.
555 *
556 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
557 * allow for the possibility of usermode upcalls messing up our count
558 * of interrupt nesting level during the busy period that is just
559 * now starting.
560 */
561void rcu_idle_exit(void)
562{
563 unsigned long flags;
564
565 local_irq_save(flags);
566 rcu_eqs_exit(false);
567 rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks), 0);
568 local_irq_restore(flags);
569}
570EXPORT_SYMBOL_GPL(rcu_idle_exit);
571
572#ifdef CONFIG_RCU_USER_QS
573/**
574 * rcu_user_exit - inform RCU that we are exiting userspace.
575 *
576 * Exit RCU idle mode while entering the kernel because it can
577 * run a RCU read side critical section anytime.
578 */
579void rcu_user_exit(void)
580{
581 rcu_eqs_exit(1);
582}
583#endif /* CONFIG_RCU_USER_QS */
584
585/**
586 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
587 *
588 * Enter an interrupt handler, which might possibly result in exiting
589 * idle mode, in other words, entering the mode in which read-side critical
590 * sections can occur.
591 *
592 * Note that the Linux kernel is fully capable of entering an interrupt
593 * handler that it never exits, for example when doing upcalls to
594 * user mode! This code assumes that the idle loop never does upcalls to
595 * user mode. If your architecture does do upcalls from the idle loop (or
596 * does anything else that results in unbalanced calls to the irq_enter()
597 * and irq_exit() functions), RCU will give you what you deserve, good
598 * and hard. But very infrequently and irreproducibly.
599 *
600 * Use things like work queues to work around this limitation.
601 *
602 * You have been warned.
603 */
604void rcu_irq_enter(void)
605{
606 unsigned long flags;
607 struct rcu_dynticks *rdtp;
608 long long oldval;
609
610 local_irq_save(flags);
611 rdtp = this_cpu_ptr(&rcu_dynticks);
612 oldval = rdtp->dynticks_nesting;
613 rdtp->dynticks_nesting++;
614 WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
615 if (oldval)
616 trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
617 else
618 rcu_eqs_exit_common(rdtp, oldval, true);
619 rcu_sysidle_exit(rdtp, 1);
620 local_irq_restore(flags);
621}
622
623/**
624 * rcu_nmi_enter - inform RCU of entry to NMI context
625 *
626 * If the CPU was idle with dynamic ticks active, and there is no
627 * irq handler running, this updates rdtp->dynticks_nmi to let the
628 * RCU grace-period handling know that the CPU is active.
629 */
630void rcu_nmi_enter(void)
631{
632 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
633
634 if (rdtp->dynticks_nmi_nesting == 0 &&
635 (atomic_read(&rdtp->dynticks) & 0x1))
636 return;
637 rdtp->dynticks_nmi_nesting++;
638 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
639 atomic_inc(&rdtp->dynticks);
640 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
641 smp_mb__after_atomic_inc(); /* See above. */
642 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
643}
644
645/**
646 * rcu_nmi_exit - inform RCU of exit from NMI context
647 *
648 * If the CPU was idle with dynamic ticks active, and there is no
649 * irq handler running, this updates rdtp->dynticks_nmi to let the
650 * RCU grace-period handling know that the CPU is no longer active.
651 */
652void rcu_nmi_exit(void)
653{
654 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
655
656 if (rdtp->dynticks_nmi_nesting == 0 ||
657 --rdtp->dynticks_nmi_nesting != 0)
658 return;
659 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
660 smp_mb__before_atomic_inc(); /* See above. */
661 atomic_inc(&rdtp->dynticks);
662 smp_mb__after_atomic_inc(); /* Force delay to next write. */
663 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
664}
665
666/**
667 * __rcu_is_watching - are RCU read-side critical sections safe?
668 *
669 * Return true if RCU is watching the running CPU, which means that
670 * this CPU can safely enter RCU read-side critical sections. Unlike
671 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
672 * least disabled preemption.
673 */
674bool notrace __rcu_is_watching(void)
675{
676 return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
677}
678
679/**
680 * rcu_is_watching - see if RCU thinks that the current CPU is idle
681 *
682 * If the current CPU is in its idle loop and is neither in an interrupt
683 * or NMI handler, return true.
684 */
685bool notrace rcu_is_watching(void)
686{
687 int ret;
688
689 preempt_disable();
690 ret = __rcu_is_watching();
691 preempt_enable();
692 return ret;
693}
694EXPORT_SYMBOL_GPL(rcu_is_watching);
695
696#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
697
698/*
699 * Is the current CPU online? Disable preemption to avoid false positives
700 * that could otherwise happen due to the current CPU number being sampled,
701 * this task being preempted, its old CPU being taken offline, resuming
702 * on some other CPU, then determining that its old CPU is now offline.
703 * It is OK to use RCU on an offline processor during initial boot, hence
704 * the check for rcu_scheduler_fully_active. Note also that it is OK
705 * for a CPU coming online to use RCU for one jiffy prior to marking itself
706 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
707 * offline to continue to use RCU for one jiffy after marking itself
708 * offline in the cpu_online_mask. This leniency is necessary given the
709 * non-atomic nature of the online and offline processing, for example,
710 * the fact that a CPU enters the scheduler after completing the CPU_DYING
711 * notifiers.
712 *
713 * This is also why RCU internally marks CPUs online during the
714 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
715 *
716 * Disable checking if in an NMI handler because we cannot safely report
717 * errors from NMI handlers anyway.
718 */
719bool rcu_lockdep_current_cpu_online(void)
720{
721 struct rcu_data *rdp;
722 struct rcu_node *rnp;
723 bool ret;
724
725 if (in_nmi())
726 return true;
727 preempt_disable();
728 rdp = this_cpu_ptr(&rcu_sched_data);
729 rnp = rdp->mynode;
730 ret = (rdp->grpmask & rnp->qsmaskinit) ||
731 !rcu_scheduler_fully_active;
732 preempt_enable();
733 return ret;
734}
735EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
736
737#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
738
739/**
740 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
741 *
742 * If the current CPU is idle or running at a first-level (not nested)
743 * interrupt from idle, return true. The caller must have at least
744 * disabled preemption.
745 */
746static int rcu_is_cpu_rrupt_from_idle(void)
747{
748 return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
749}
750
751/*
752 * Snapshot the specified CPU's dynticks counter so that we can later
753 * credit them with an implicit quiescent state. Return 1 if this CPU
754 * is in dynticks idle mode, which is an extended quiescent state.
755 */
756static int dyntick_save_progress_counter(struct rcu_data *rdp,
757 bool *isidle, unsigned long *maxj)
758{
759 rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
760 rcu_sysidle_check_cpu(rdp, isidle, maxj);
761 return (rdp->dynticks_snap & 0x1) == 0;
762}
763
764/*
765 * This function really isn't for public consumption, but RCU is special in
766 * that context switches can allow the state machine to make progress.
767 */
768extern void resched_cpu(int cpu);
769
770/*
771 * Return true if the specified CPU has passed through a quiescent
772 * state by virtue of being in or having passed through an dynticks
773 * idle state since the last call to dyntick_save_progress_counter()
774 * for this same CPU, or by virtue of having been offline.
775 */
776static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
777 bool *isidle, unsigned long *maxj)
778{
779 unsigned int curr;
780 unsigned int snap;
781
782 curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
783 snap = (unsigned int)rdp->dynticks_snap;
784
785 /*
786 * If the CPU passed through or entered a dynticks idle phase with
787 * no active irq/NMI handlers, then we can safely pretend that the CPU
788 * already acknowledged the request to pass through a quiescent
789 * state. Either way, that CPU cannot possibly be in an RCU
790 * read-side critical section that started before the beginning
791 * of the current RCU grace period.
792 */
793 if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
794 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
795 rdp->dynticks_fqs++;
796 return 1;
797 }
798
799 /*
800 * Check for the CPU being offline, but only if the grace period
801 * is old enough. We don't need to worry about the CPU changing
802 * state: If we see it offline even once, it has been through a
803 * quiescent state.
804 *
805 * The reason for insisting that the grace period be at least
806 * one jiffy old is that CPUs that are not quite online and that
807 * have just gone offline can still execute RCU read-side critical
808 * sections.
809 */
810 if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
811 return 0; /* Grace period is not old enough. */
812 barrier();
813 if (cpu_is_offline(rdp->cpu)) {
814 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
815 rdp->offline_fqs++;
816 return 1;
817 }
818
819 /*
820 * There is a possibility that a CPU in adaptive-ticks state
821 * might run in the kernel with the scheduling-clock tick disabled
822 * for an extended time period. Invoke rcu_kick_nohz_cpu() to
823 * force the CPU to restart the scheduling-clock tick in this
824 * CPU is in this state.
825 */
826 rcu_kick_nohz_cpu(rdp->cpu);
827
828 /*
829 * Alternatively, the CPU might be running in the kernel
830 * for an extended period of time without a quiescent state.
831 * Attempt to force the CPU through the scheduler to gain the
832 * needed quiescent state, but only if the grace period has gone
833 * on for an uncommonly long time. If there are many stuck CPUs,
834 * we will beat on the first one until it gets unstuck, then move
835 * to the next. Only do this for the primary flavor of RCU.
836 */
837 if (rdp->rsp == rcu_state &&
838 ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
839 rdp->rsp->jiffies_resched += 5;
840 resched_cpu(rdp->cpu);
841 }
842
843 return 0;
844}
845
846static void record_gp_stall_check_time(struct rcu_state *rsp)
847{
848 unsigned long j = jiffies;
849 unsigned long j1;
850
851 rsp->gp_start = j;
852 smp_wmb(); /* Record start time before stall time. */
853 j1 = rcu_jiffies_till_stall_check();
854 rsp->jiffies_stall = j + j1;
855 rsp->jiffies_resched = j + j1 / 2;
856}
857
858/*
859 * Dump stacks of all tasks running on stalled CPUs. This is a fallback
860 * for architectures that do not implement trigger_all_cpu_backtrace().
861 * The NMI-triggered stack traces are more accurate because they are
862 * printed by the target CPU.
863 */
864static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
865{
866 int cpu;
867 unsigned long flags;
868 struct rcu_node *rnp;
869
870 rcu_for_each_leaf_node(rsp, rnp) {
871 raw_spin_lock_irqsave(&rnp->lock, flags);
872 if (rnp->qsmask != 0) {
873 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
874 if (rnp->qsmask & (1UL << cpu))
875 dump_cpu_task(rnp->grplo + cpu);
876 }
877 raw_spin_unlock_irqrestore(&rnp->lock, flags);
878 }
879}
880
881static void print_other_cpu_stall(struct rcu_state *rsp)
882{
883 int cpu;
884 long delta;
885 unsigned long flags;
886 int ndetected = 0;
887 struct rcu_node *rnp = rcu_get_root(rsp);
888 long totqlen = 0;
889
890 /* Only let one CPU complain about others per time interval. */
891
892 raw_spin_lock_irqsave(&rnp->lock, flags);
893 delta = jiffies - rsp->jiffies_stall;
894 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
895 raw_spin_unlock_irqrestore(&rnp->lock, flags);
896 return;
897 }
898 rsp->jiffies_stall = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
899 raw_spin_unlock_irqrestore(&rnp->lock, flags);
900
901 /*
902 * OK, time to rat on our buddy...
903 * See Documentation/RCU/stallwarn.txt for info on how to debug
904 * RCU CPU stall warnings.
905 */
906 pr_err("INFO: %s detected stalls on CPUs/tasks:",
907 rsp->name);
908 print_cpu_stall_info_begin();
909 rcu_for_each_leaf_node(rsp, rnp) {
910 raw_spin_lock_irqsave(&rnp->lock, flags);
911 ndetected += rcu_print_task_stall(rnp);
912 if (rnp->qsmask != 0) {
913 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
914 if (rnp->qsmask & (1UL << cpu)) {
915 print_cpu_stall_info(rsp,
916 rnp->grplo + cpu);
917 ndetected++;
918 }
919 }
920 raw_spin_unlock_irqrestore(&rnp->lock, flags);
921 }
922
923 /*
924 * Now rat on any tasks that got kicked up to the root rcu_node
925 * due to CPU offlining.
926 */
927 rnp = rcu_get_root(rsp);
928 raw_spin_lock_irqsave(&rnp->lock, flags);
929 ndetected += rcu_print_task_stall(rnp);
930 raw_spin_unlock_irqrestore(&rnp->lock, flags);
931
932 print_cpu_stall_info_end();
933 for_each_possible_cpu(cpu)
934 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
935 pr_cont("(detected by %d, t=%ld jiffies, g=%lu, c=%lu, q=%lu)\n",
936 smp_processor_id(), (long)(jiffies - rsp->gp_start),
937 rsp->gpnum, rsp->completed, totqlen);
938 if (ndetected == 0)
939 pr_err("INFO: Stall ended before state dump start\n");
940 else if (!trigger_all_cpu_backtrace())
941 rcu_dump_cpu_stacks(rsp);
942
943 /* Complain about tasks blocking the grace period. */
944
945 rcu_print_detail_task_stall(rsp);
946
947 force_quiescent_state(rsp); /* Kick them all. */
948}
949
950/*
951 * This function really isn't for public consumption, but RCU is special in
952 * that context switches can allow the state machine to make progress.
953 */
954extern void resched_cpu(int cpu);
955
956static void print_cpu_stall(struct rcu_state *rsp)
957{
958 int cpu;
959 unsigned long flags;
960 struct rcu_node *rnp = rcu_get_root(rsp);
961 long totqlen = 0;
962
963 /*
964 * OK, time to rat on ourselves...
965 * See Documentation/RCU/stallwarn.txt for info on how to debug
966 * RCU CPU stall warnings.
967 */
968 pr_err("INFO: %s self-detected stall on CPU", rsp->name);
969 print_cpu_stall_info_begin();
970 print_cpu_stall_info(rsp, smp_processor_id());
971 print_cpu_stall_info_end();
972 for_each_possible_cpu(cpu)
973 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
974 pr_cont(" (t=%lu jiffies g=%lu c=%lu q=%lu)\n",
975 jiffies - rsp->gp_start, rsp->gpnum, rsp->completed, totqlen);
976 if (!trigger_all_cpu_backtrace())
977 dump_stack();
978
979 raw_spin_lock_irqsave(&rnp->lock, flags);
980 if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
981 rsp->jiffies_stall = jiffies +
982 3 * rcu_jiffies_till_stall_check() + 3;
983 raw_spin_unlock_irqrestore(&rnp->lock, flags);
984
985 /*
986 * Attempt to revive the RCU machinery by forcing a context switch.
987 *
988 * A context switch would normally allow the RCU state machine to make
989 * progress and it could be we're stuck in kernel space without context
990 * switches for an entirely unreasonable amount of time.
991 */
992 resched_cpu(smp_processor_id());
993}
994
995static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
996{
997 unsigned long completed;
998 unsigned long gpnum;
999 unsigned long gps;
1000 unsigned long j;
1001 unsigned long js;
1002 struct rcu_node *rnp;
1003
1004 if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1005 return;
1006 j = jiffies;
1007
1008 /*
1009 * Lots of memory barriers to reject false positives.
1010 *
1011 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1012 * then rsp->gp_start, and finally rsp->completed. These values
1013 * are updated in the opposite order with memory barriers (or
1014 * equivalent) during grace-period initialization and cleanup.
1015 * Now, a false positive can occur if we get an new value of
1016 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
1017 * the memory barriers, the only way that this can happen is if one
1018 * grace period ends and another starts between these two fetches.
1019 * Detect this by comparing rsp->completed with the previous fetch
1020 * from rsp->gpnum.
1021 *
1022 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1023 * and rsp->gp_start suffice to forestall false positives.
1024 */
1025 gpnum = ACCESS_ONCE(rsp->gpnum);
1026 smp_rmb(); /* Pick up ->gpnum first... */
1027 js = ACCESS_ONCE(rsp->jiffies_stall);
1028 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1029 gps = ACCESS_ONCE(rsp->gp_start);
1030 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1031 completed = ACCESS_ONCE(rsp->completed);
1032 if (ULONG_CMP_GE(completed, gpnum) ||
1033 ULONG_CMP_LT(j, js) ||
1034 ULONG_CMP_GE(gps, js))
1035 return; /* No stall or GP completed since entering function. */
1036 rnp = rdp->mynode;
1037 if (rcu_gp_in_progress(rsp) &&
1038 (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask)) {
1039
1040 /* We haven't checked in, so go dump stack. */
1041 print_cpu_stall(rsp);
1042
1043 } else if (rcu_gp_in_progress(rsp) &&
1044 ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1045
1046 /* They had a few time units to dump stack, so complain. */
1047 print_other_cpu_stall(rsp);
1048 }
1049}
1050
1051/**
1052 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1053 *
1054 * Set the stall-warning timeout way off into the future, thus preventing
1055 * any RCU CPU stall-warning messages from appearing in the current set of
1056 * RCU grace periods.
1057 *
1058 * The caller must disable hard irqs.
1059 */
1060void rcu_cpu_stall_reset(void)
1061{
1062 struct rcu_state *rsp;
1063
1064 for_each_rcu_flavor(rsp)
1065 rsp->jiffies_stall = jiffies + ULONG_MAX / 2;
1066}
1067
1068/*
1069 * Initialize the specified rcu_data structure's callback list to empty.
1070 */
1071static void init_callback_list(struct rcu_data *rdp)
1072{
1073 int i;
1074
1075 if (init_nocb_callback_list(rdp))
1076 return;
1077 rdp->nxtlist = NULL;
1078 for (i = 0; i < RCU_NEXT_SIZE; i++)
1079 rdp->nxttail[i] = &rdp->nxtlist;
1080}
1081
1082/*
1083 * Determine the value that ->completed will have at the end of the
1084 * next subsequent grace period. This is used to tag callbacks so that
1085 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1086 * been dyntick-idle for an extended period with callbacks under the
1087 * influence of RCU_FAST_NO_HZ.
1088 *
1089 * The caller must hold rnp->lock with interrupts disabled.
1090 */
1091static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
1092 struct rcu_node *rnp)
1093{
1094 /*
1095 * If RCU is idle, we just wait for the next grace period.
1096 * But we can only be sure that RCU is idle if we are looking
1097 * at the root rcu_node structure -- otherwise, a new grace
1098 * period might have started, but just not yet gotten around
1099 * to initializing the current non-root rcu_node structure.
1100 */
1101 if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
1102 return rnp->completed + 1;
1103
1104 /*
1105 * Otherwise, wait for a possible partial grace period and
1106 * then the subsequent full grace period.
1107 */
1108 return rnp->completed + 2;
1109}
1110
1111/*
1112 * Trace-event helper function for rcu_start_future_gp() and
1113 * rcu_nocb_wait_gp().
1114 */
1115static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1116 unsigned long c, const char *s)
1117{
1118 trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
1119 rnp->completed, c, rnp->level,
1120 rnp->grplo, rnp->grphi, s);
1121}
1122
1123/*
1124 * Start some future grace period, as needed to handle newly arrived
1125 * callbacks. The required future grace periods are recorded in each
1126 * rcu_node structure's ->need_future_gp field.
1127 *
1128 * The caller must hold the specified rcu_node structure's ->lock.
1129 */
1130static unsigned long __maybe_unused
1131rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp)
1132{
1133 unsigned long c;
1134 int i;
1135 struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
1136
1137 /*
1138 * Pick up grace-period number for new callbacks. If this
1139 * grace period is already marked as needed, return to the caller.
1140 */
1141 c = rcu_cbs_completed(rdp->rsp, rnp);
1142 trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1143 if (rnp->need_future_gp[c & 0x1]) {
1144 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1145 return c;
1146 }
1147
1148 /*
1149 * If either this rcu_node structure or the root rcu_node structure
1150 * believe that a grace period is in progress, then we must wait
1151 * for the one following, which is in "c". Because our request
1152 * will be noticed at the end of the current grace period, we don't
1153 * need to explicitly start one.
1154 */
1155 if (rnp->gpnum != rnp->completed ||
1156 ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) {
1157 rnp->need_future_gp[c & 0x1]++;
1158 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1159 return c;
1160 }
1161
1162 /*
1163 * There might be no grace period in progress. If we don't already
1164 * hold it, acquire the root rcu_node structure's lock in order to
1165 * start one (if needed).
1166 */
1167 if (rnp != rnp_root) {
1168 raw_spin_lock(&rnp_root->lock);
1169 smp_mb__after_unlock_lock();
1170 }
1171
1172 /*
1173 * Get a new grace-period number. If there really is no grace
1174 * period in progress, it will be smaller than the one we obtained
1175 * earlier. Adjust callbacks as needed. Note that even no-CBs
1176 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1177 */
1178 c = rcu_cbs_completed(rdp->rsp, rnp_root);
1179 for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
1180 if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
1181 rdp->nxtcompleted[i] = c;
1182
1183 /*
1184 * If the needed for the required grace period is already
1185 * recorded, trace and leave.
1186 */
1187 if (rnp_root->need_future_gp[c & 0x1]) {
1188 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1189 goto unlock_out;
1190 }
1191
1192 /* Record the need for the future grace period. */
1193 rnp_root->need_future_gp[c & 0x1]++;
1194
1195 /* If a grace period is not already in progress, start one. */
1196 if (rnp_root->gpnum != rnp_root->completed) {
1197 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1198 } else {
1199 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1200 rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1201 }
1202unlock_out:
1203 if (rnp != rnp_root)
1204 raw_spin_unlock(&rnp_root->lock);
1205 return c;
1206}
1207
1208/*
1209 * Clean up any old requests for the just-ended grace period. Also return
1210 * whether any additional grace periods have been requested. Also invoke
1211 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1212 * waiting for this grace period to complete.
1213 */
1214static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1215{
1216 int c = rnp->completed;
1217 int needmore;
1218 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1219
1220 rcu_nocb_gp_cleanup(rsp, rnp);
1221 rnp->need_future_gp[c & 0x1] = 0;
1222 needmore = rnp->need_future_gp[(c + 1) & 0x1];
1223 trace_rcu_future_gp(rnp, rdp, c,
1224 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1225 return needmore;
1226}
1227
1228/*
1229 * If there is room, assign a ->completed number to any callbacks on
1230 * this CPU that have not already been assigned. Also accelerate any
1231 * callbacks that were previously assigned a ->completed number that has
1232 * since proven to be too conservative, which can happen if callbacks get
1233 * assigned a ->completed number while RCU is idle, but with reference to
1234 * a non-root rcu_node structure. This function is idempotent, so it does
1235 * not hurt to call it repeatedly.
1236 *
1237 * The caller must hold rnp->lock with interrupts disabled.
1238 */
1239static void rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1240 struct rcu_data *rdp)
1241{
1242 unsigned long c;
1243 int i;
1244
1245 /* If the CPU has no callbacks, nothing to do. */
1246 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1247 return;
1248
1249 /*
1250 * Starting from the sublist containing the callbacks most
1251 * recently assigned a ->completed number and working down, find the
1252 * first sublist that is not assignable to an upcoming grace period.
1253 * Such a sublist has something in it (first two tests) and has
1254 * a ->completed number assigned that will complete sooner than
1255 * the ->completed number for newly arrived callbacks (last test).
1256 *
1257 * The key point is that any later sublist can be assigned the
1258 * same ->completed number as the newly arrived callbacks, which
1259 * means that the callbacks in any of these later sublist can be
1260 * grouped into a single sublist, whether or not they have already
1261 * been assigned a ->completed number.
1262 */
1263 c = rcu_cbs_completed(rsp, rnp);
1264 for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
1265 if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
1266 !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
1267 break;
1268
1269 /*
1270 * If there are no sublist for unassigned callbacks, leave.
1271 * At the same time, advance "i" one sublist, so that "i" will
1272 * index into the sublist where all the remaining callbacks should
1273 * be grouped into.
1274 */
1275 if (++i >= RCU_NEXT_TAIL)
1276 return;
1277
1278 /*
1279 * Assign all subsequent callbacks' ->completed number to the next
1280 * full grace period and group them all in the sublist initially
1281 * indexed by "i".
1282 */
1283 for (; i <= RCU_NEXT_TAIL; i++) {
1284 rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
1285 rdp->nxtcompleted[i] = c;
1286 }
1287 /* Record any needed additional grace periods. */
1288 rcu_start_future_gp(rnp, rdp);
1289
1290 /* Trace depending on how much we were able to accelerate. */
1291 if (!*rdp->nxttail[RCU_WAIT_TAIL])
1292 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1293 else
1294 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1295}
1296
1297/*
1298 * Move any callbacks whose grace period has completed to the
1299 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1300 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1301 * sublist. This function is idempotent, so it does not hurt to
1302 * invoke it repeatedly. As long as it is not invoked -too- often...
1303 *
1304 * The caller must hold rnp->lock with interrupts disabled.
1305 */
1306static void rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1307 struct rcu_data *rdp)
1308{
1309 int i, j;
1310
1311 /* If the CPU has no callbacks, nothing to do. */
1312 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1313 return;
1314
1315 /*
1316 * Find all callbacks whose ->completed numbers indicate that they
1317 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1318 */
1319 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
1320 if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
1321 break;
1322 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
1323 }
1324 /* Clean up any sublist tail pointers that were misordered above. */
1325 for (j = RCU_WAIT_TAIL; j < i; j++)
1326 rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
1327
1328 /* Copy down callbacks to fill in empty sublists. */
1329 for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
1330 if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
1331 break;
1332 rdp->nxttail[j] = rdp->nxttail[i];
1333 rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
1334 }
1335
1336 /* Classify any remaining callbacks. */
1337 rcu_accelerate_cbs(rsp, rnp, rdp);
1338}
1339
1340/*
1341 * Update CPU-local rcu_data state to record the beginnings and ends of
1342 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1343 * structure corresponding to the current CPU, and must have irqs disabled.
1344 */
1345static void __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
1346{
1347 /* Handle the ends of any preceding grace periods first. */
1348 if (rdp->completed == rnp->completed) {
1349
1350 /* No grace period end, so just accelerate recent callbacks. */
1351 rcu_accelerate_cbs(rsp, rnp, rdp);
1352
1353 } else {
1354
1355 /* Advance callbacks. */
1356 rcu_advance_cbs(rsp, rnp, rdp);
1357
1358 /* Remember that we saw this grace-period completion. */
1359 rdp->completed = rnp->completed;
1360 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1361 }
1362
1363 if (rdp->gpnum != rnp->gpnum) {
1364 /*
1365 * If the current grace period is waiting for this CPU,
1366 * set up to detect a quiescent state, otherwise don't
1367 * go looking for one.
1368 */
1369 rdp->gpnum = rnp->gpnum;
1370 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1371 rdp->passed_quiesce = 0;
1372 rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
1373 zero_cpu_stall_ticks(rdp);
1374 }
1375}
1376
1377static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1378{
1379 unsigned long flags;
1380 struct rcu_node *rnp;
1381
1382 local_irq_save(flags);
1383 rnp = rdp->mynode;
1384 if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
1385 rdp->completed == ACCESS_ONCE(rnp->completed)) || /* w/out lock. */
1386 !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
1387 local_irq_restore(flags);
1388 return;
1389 }
1390 smp_mb__after_unlock_lock();
1391 __note_gp_changes(rsp, rnp, rdp);
1392 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1393}
1394
1395/*
1396 * Initialize a new grace period. Return 0 if no grace period required.
1397 */
1398static int rcu_gp_init(struct rcu_state *rsp)
1399{
1400 struct rcu_data *rdp;
1401 struct rcu_node *rnp = rcu_get_root(rsp);
1402
1403 rcu_bind_gp_kthread();
1404 raw_spin_lock_irq(&rnp->lock);
1405 smp_mb__after_unlock_lock();
1406 if (rsp->gp_flags == 0) {
1407 /* Spurious wakeup, tell caller to go back to sleep. */
1408 raw_spin_unlock_irq(&rnp->lock);
1409 return 0;
1410 }
1411 rsp->gp_flags = 0; /* Clear all flags: New grace period. */
1412
1413 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
1414 /*
1415 * Grace period already in progress, don't start another.
1416 * Not supposed to be able to happen.
1417 */
1418 raw_spin_unlock_irq(&rnp->lock);
1419 return 0;
1420 }
1421
1422 /* Advance to a new grace period and initialize state. */
1423 record_gp_stall_check_time(rsp);
1424 /* Record GP times before starting GP, hence smp_store_release(). */
1425 smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1426 trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1427 raw_spin_unlock_irq(&rnp->lock);
1428
1429 /* Exclude any concurrent CPU-hotplug operations. */
1430 mutex_lock(&rsp->onoff_mutex);
1431 smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */
1432
1433 /*
1434 * Set the quiescent-state-needed bits in all the rcu_node
1435 * structures for all currently online CPUs in breadth-first order,
1436 * starting from the root rcu_node structure, relying on the layout
1437 * of the tree within the rsp->node[] array. Note that other CPUs
1438 * will access only the leaves of the hierarchy, thus seeing that no
1439 * grace period is in progress, at least until the corresponding
1440 * leaf node has been initialized. In addition, we have excluded
1441 * CPU-hotplug operations.
1442 *
1443 * The grace period cannot complete until the initialization
1444 * process finishes, because this kthread handles both.
1445 */
1446 rcu_for_each_node_breadth_first(rsp, rnp) {
1447 raw_spin_lock_irq(&rnp->lock);
1448 smp_mb__after_unlock_lock();
1449 rdp = this_cpu_ptr(rsp->rda);
1450 rcu_preempt_check_blocked_tasks(rnp);
1451 rnp->qsmask = rnp->qsmaskinit;
1452 ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
1453 WARN_ON_ONCE(rnp->completed != rsp->completed);
1454 ACCESS_ONCE(rnp->completed) = rsp->completed;
1455 if (rnp == rdp->mynode)
1456 __note_gp_changes(rsp, rnp, rdp);
1457 rcu_preempt_boost_start_gp(rnp);
1458 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
1459 rnp->level, rnp->grplo,
1460 rnp->grphi, rnp->qsmask);
1461 raw_spin_unlock_irq(&rnp->lock);
1462#ifdef CONFIG_PROVE_RCU_DELAY
1463 if ((prandom_u32() % (rcu_num_nodes + 1)) == 0 &&
1464 system_state == SYSTEM_RUNNING)
1465 udelay(200);
1466#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1467 cond_resched();
1468 }
1469
1470 mutex_unlock(&rsp->onoff_mutex);
1471 return 1;
1472}
1473
1474/*
1475 * Do one round of quiescent-state forcing.
1476 */
1477static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1478{
1479 int fqs_state = fqs_state_in;
1480 bool isidle = false;
1481 unsigned long maxj;
1482 struct rcu_node *rnp = rcu_get_root(rsp);
1483
1484 rsp->n_force_qs++;
1485 if (fqs_state == RCU_SAVE_DYNTICK) {
1486 /* Collect dyntick-idle snapshots. */
1487 if (is_sysidle_rcu_state(rsp)) {
1488 isidle = 1;
1489 maxj = jiffies - ULONG_MAX / 4;
1490 }
1491 force_qs_rnp(rsp, dyntick_save_progress_counter,
1492 &isidle, &maxj);
1493 rcu_sysidle_report_gp(rsp, isidle, maxj);
1494 fqs_state = RCU_FORCE_QS;
1495 } else {
1496 /* Handle dyntick-idle and offline CPUs. */
1497 isidle = 0;
1498 force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1499 }
1500 /* Clear flag to prevent immediate re-entry. */
1501 if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
1502 raw_spin_lock_irq(&rnp->lock);
1503 smp_mb__after_unlock_lock();
1504 rsp->gp_flags &= ~RCU_GP_FLAG_FQS;
1505 raw_spin_unlock_irq(&rnp->lock);
1506 }
1507 return fqs_state;
1508}
1509
1510/*
1511 * Clean up after the old grace period.
1512 */
1513static void rcu_gp_cleanup(struct rcu_state *rsp)
1514{
1515 unsigned long gp_duration;
1516 int nocb = 0;
1517 struct rcu_data *rdp;
1518 struct rcu_node *rnp = rcu_get_root(rsp);
1519
1520 raw_spin_lock_irq(&rnp->lock);
1521 smp_mb__after_unlock_lock();
1522 gp_duration = jiffies - rsp->gp_start;
1523 if (gp_duration > rsp->gp_max)
1524 rsp->gp_max = gp_duration;
1525
1526 /*
1527 * We know the grace period is complete, but to everyone else
1528 * it appears to still be ongoing. But it is also the case
1529 * that to everyone else it looks like there is nothing that
1530 * they can do to advance the grace period. It is therefore
1531 * safe for us to drop the lock in order to mark the grace
1532 * period as completed in all of the rcu_node structures.
1533 */
1534 raw_spin_unlock_irq(&rnp->lock);
1535
1536 /*
1537 * Propagate new ->completed value to rcu_node structures so
1538 * that other CPUs don't have to wait until the start of the next
1539 * grace period to process their callbacks. This also avoids
1540 * some nasty RCU grace-period initialization races by forcing
1541 * the end of the current grace period to be completely recorded in
1542 * all of the rcu_node structures before the beginning of the next
1543 * grace period is recorded in any of the rcu_node structures.
1544 */
1545 rcu_for_each_node_breadth_first(rsp, rnp) {
1546 raw_spin_lock_irq(&rnp->lock);
1547 smp_mb__after_unlock_lock();
1548 ACCESS_ONCE(rnp->completed) = rsp->gpnum;
1549 rdp = this_cpu_ptr(rsp->rda);
1550 if (rnp == rdp->mynode)
1551 __note_gp_changes(rsp, rnp, rdp);
1552 /* smp_mb() provided by prior unlock-lock pair. */
1553 nocb += rcu_future_gp_cleanup(rsp, rnp);
1554 raw_spin_unlock_irq(&rnp->lock);
1555 cond_resched();
1556 }
1557 rnp = rcu_get_root(rsp);
1558 raw_spin_lock_irq(&rnp->lock);
1559 smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
1560 rcu_nocb_gp_set(rnp, nocb);
1561
1562 /* Declare grace period done. */
1563 ACCESS_ONCE(rsp->completed) = rsp->gpnum;
1564 trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
1565 rsp->fqs_state = RCU_GP_IDLE;
1566 rdp = this_cpu_ptr(rsp->rda);
1567 rcu_advance_cbs(rsp, rnp, rdp); /* Reduce false positives below. */
1568 if (cpu_needs_another_gp(rsp, rdp)) {
1569 rsp->gp_flags = RCU_GP_FLAG_INIT;
1570 trace_rcu_grace_period(rsp->name,
1571 ACCESS_ONCE(rsp->gpnum),
1572 TPS("newreq"));
1573 }
1574 raw_spin_unlock_irq(&rnp->lock);
1575}
1576
1577/*
1578 * Body of kthread that handles grace periods.
1579 */
1580static int __noreturn rcu_gp_kthread(void *arg)
1581{
1582 int fqs_state;
1583 int gf;
1584 unsigned long j;
1585 int ret;
1586 struct rcu_state *rsp = arg;
1587 struct rcu_node *rnp = rcu_get_root(rsp);
1588
1589 for (;;) {
1590
1591 /* Handle grace-period start. */
1592 for (;;) {
1593 trace_rcu_grace_period(rsp->name,
1594 ACCESS_ONCE(rsp->gpnum),
1595 TPS("reqwait"));
1596 wait_event_interruptible(rsp->gp_wq,
1597 ACCESS_ONCE(rsp->gp_flags) &
1598 RCU_GP_FLAG_INIT);
1599 /* Locking provides needed memory barrier. */
1600 if (rcu_gp_init(rsp))
1601 break;
1602 cond_resched();
1603 flush_signals(current);
1604 trace_rcu_grace_period(rsp->name,
1605 ACCESS_ONCE(rsp->gpnum),
1606 TPS("reqwaitsig"));
1607 }
1608
1609 /* Handle quiescent-state forcing. */
1610 fqs_state = RCU_SAVE_DYNTICK;
1611 j = jiffies_till_first_fqs;
1612 if (j > HZ) {
1613 j = HZ;
1614 jiffies_till_first_fqs = HZ;
1615 }
1616 ret = 0;
1617 for (;;) {
1618 if (!ret)
1619 rsp->jiffies_force_qs = jiffies + j;
1620 trace_rcu_grace_period(rsp->name,
1621 ACCESS_ONCE(rsp->gpnum),
1622 TPS("fqswait"));
1623 ret = wait_event_interruptible_timeout(rsp->gp_wq,
1624 ((gf = ACCESS_ONCE(rsp->gp_flags)) &
1625 RCU_GP_FLAG_FQS) ||
1626 (!ACCESS_ONCE(rnp->qsmask) &&
1627 !rcu_preempt_blocked_readers_cgp(rnp)),
1628 j);
1629 /* Locking provides needed memory barriers. */
1630 /* If grace period done, leave loop. */
1631 if (!ACCESS_ONCE(rnp->qsmask) &&
1632 !rcu_preempt_blocked_readers_cgp(rnp))
1633 break;
1634 /* If time for quiescent-state forcing, do it. */
1635 if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
1636 (gf & RCU_GP_FLAG_FQS)) {
1637 trace_rcu_grace_period(rsp->name,
1638 ACCESS_ONCE(rsp->gpnum),
1639 TPS("fqsstart"));
1640 fqs_state = rcu_gp_fqs(rsp, fqs_state);
1641 trace_rcu_grace_period(rsp->name,
1642 ACCESS_ONCE(rsp->gpnum),
1643 TPS("fqsend"));
1644 cond_resched();
1645 } else {
1646 /* Deal with stray signal. */
1647 cond_resched();
1648 flush_signals(current);
1649 trace_rcu_grace_period(rsp->name,
1650 ACCESS_ONCE(rsp->gpnum),
1651 TPS("fqswaitsig"));
1652 }
1653 j = jiffies_till_next_fqs;
1654 if (j > HZ) {
1655 j = HZ;
1656 jiffies_till_next_fqs = HZ;
1657 } else if (j < 1) {
1658 j = 1;
1659 jiffies_till_next_fqs = 1;
1660 }
1661 }
1662
1663 /* Handle grace-period end. */
1664 rcu_gp_cleanup(rsp);
1665 }
1666}
1667
1668static void rsp_wakeup(struct irq_work *work)
1669{
1670 struct rcu_state *rsp = container_of(work, struct rcu_state, wakeup_work);
1671
1672 /* Wake up rcu_gp_kthread() to start the grace period. */
1673 wake_up(&rsp->gp_wq);
1674}
1675
1676/*
1677 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1678 * in preparation for detecting the next grace period. The caller must hold
1679 * the root node's ->lock and hard irqs must be disabled.
1680 *
1681 * Note that it is legal for a dying CPU (which is marked as offline) to
1682 * invoke this function. This can happen when the dying CPU reports its
1683 * quiescent state.
1684 */
1685static void
1686rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
1687 struct rcu_data *rdp)
1688{
1689 if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
1690 /*
1691 * Either we have not yet spawned the grace-period
1692 * task, this CPU does not need another grace period,
1693 * or a grace period is already in progress.
1694 * Either way, don't start a new grace period.
1695 */
1696 return;
1697 }
1698 rsp->gp_flags = RCU_GP_FLAG_INIT;
1699 trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
1700 TPS("newreq"));
1701
1702 /*
1703 * We can't do wakeups while holding the rnp->lock, as that
1704 * could cause possible deadlocks with the rq->lock. Defer
1705 * the wakeup to interrupt context. And don't bother waking
1706 * up the running kthread.
1707 */
1708 if (current != rsp->gp_kthread)
1709 irq_work_queue(&rsp->wakeup_work);
1710}
1711
1712/*
1713 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
1714 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
1715 * is invoked indirectly from rcu_advance_cbs(), which would result in
1716 * endless recursion -- or would do so if it wasn't for the self-deadlock
1717 * that is encountered beforehand.
1718 */
1719static void
1720rcu_start_gp(struct rcu_state *rsp)
1721{
1722 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1723 struct rcu_node *rnp = rcu_get_root(rsp);
1724
1725 /*
1726 * If there is no grace period in progress right now, any
1727 * callbacks we have up to this point will be satisfied by the
1728 * next grace period. Also, advancing the callbacks reduces the
1729 * probability of false positives from cpu_needs_another_gp()
1730 * resulting in pointless grace periods. So, advance callbacks
1731 * then start the grace period!
1732 */
1733 rcu_advance_cbs(rsp, rnp, rdp);
1734 rcu_start_gp_advanced(rsp, rnp, rdp);
1735}
1736
1737/*
1738 * Report a full set of quiescent states to the specified rcu_state
1739 * data structure. This involves cleaning up after the prior grace
1740 * period and letting rcu_start_gp() start up the next grace period
1741 * if one is needed. Note that the caller must hold rnp->lock, which
1742 * is released before return.
1743 */
1744static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
1745 __releases(rcu_get_root(rsp)->lock)
1746{
1747 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
1748 raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
1749 wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
1750}
1751
1752/*
1753 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1754 * Allows quiescent states for a group of CPUs to be reported at one go
1755 * to the specified rcu_node structure, though all the CPUs in the group
1756 * must be represented by the same rcu_node structure (which need not be
1757 * a leaf rcu_node structure, though it often will be). That structure's
1758 * lock must be held upon entry, and it is released before return.
1759 */
1760static void
1761rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
1762 struct rcu_node *rnp, unsigned long flags)
1763 __releases(rnp->lock)
1764{
1765 struct rcu_node *rnp_c;
1766
1767 /* Walk up the rcu_node hierarchy. */
1768 for (;;) {
1769 if (!(rnp->qsmask & mask)) {
1770
1771 /* Our bit has already been cleared, so done. */
1772 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1773 return;
1774 }
1775 rnp->qsmask &= ~mask;
1776 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
1777 mask, rnp->qsmask, rnp->level,
1778 rnp->grplo, rnp->grphi,
1779 !!rnp->gp_tasks);
1780 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1781
1782 /* Other bits still set at this level, so done. */
1783 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1784 return;
1785 }
1786 mask = rnp->grpmask;
1787 if (rnp->parent == NULL) {
1788
1789 /* No more levels. Exit loop holding root lock. */
1790
1791 break;
1792 }
1793 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1794 rnp_c = rnp;
1795 rnp = rnp->parent;
1796 raw_spin_lock_irqsave(&rnp->lock, flags);
1797 smp_mb__after_unlock_lock();
1798 WARN_ON_ONCE(rnp_c->qsmask);
1799 }
1800
1801 /*
1802 * Get here if we are the last CPU to pass through a quiescent
1803 * state for this grace period. Invoke rcu_report_qs_rsp()
1804 * to clean up and start the next grace period if one is needed.
1805 */
1806 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
1807}
1808
1809/*
1810 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1811 * structure. This must be either called from the specified CPU, or
1812 * called when the specified CPU is known to be offline (and when it is
1813 * also known that no other CPU is concurrently trying to help the offline
1814 * CPU). The lastcomp argument is used to make sure we are still in the
1815 * grace period of interest. We don't want to end the current grace period
1816 * based on quiescent states detected in an earlier grace period!
1817 */
1818static void
1819rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
1820{
1821 unsigned long flags;
1822 unsigned long mask;
1823 struct rcu_node *rnp;
1824
1825 rnp = rdp->mynode;
1826 raw_spin_lock_irqsave(&rnp->lock, flags);
1827 smp_mb__after_unlock_lock();
1828 if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
1829 rnp->completed == rnp->gpnum) {
1830
1831 /*
1832 * The grace period in which this quiescent state was
1833 * recorded has ended, so don't report it upwards.
1834 * We will instead need a new quiescent state that lies
1835 * within the current grace period.
1836 */
1837 rdp->passed_quiesce = 0; /* need qs for new gp. */
1838 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1839 return;
1840 }
1841 mask = rdp->grpmask;
1842 if ((rnp->qsmask & mask) == 0) {
1843 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1844 } else {
1845 rdp->qs_pending = 0;
1846
1847 /*
1848 * This GP can't end until cpu checks in, so all of our
1849 * callbacks can be processed during the next GP.
1850 */
1851 rcu_accelerate_cbs(rsp, rnp, rdp);
1852
1853 rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
1854 }
1855}
1856
1857/*
1858 * Check to see if there is a new grace period of which this CPU
1859 * is not yet aware, and if so, set up local rcu_data state for it.
1860 * Otherwise, see if this CPU has just passed through its first
1861 * quiescent state for this grace period, and record that fact if so.
1862 */
1863static void
1864rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
1865{
1866 /* Check for grace-period ends and beginnings. */
1867 note_gp_changes(rsp, rdp);
1868
1869 /*
1870 * Does this CPU still need to do its part for current grace period?
1871 * If no, return and let the other CPUs do their part as well.
1872 */
1873 if (!rdp->qs_pending)
1874 return;
1875
1876 /*
1877 * Was there a quiescent state since the beginning of the grace
1878 * period? If no, then exit and wait for the next call.
1879 */
1880 if (!rdp->passed_quiesce)
1881 return;
1882
1883 /*
1884 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1885 * judge of that).
1886 */
1887 rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
1888}
1889
1890#ifdef CONFIG_HOTPLUG_CPU
1891
1892/*
1893 * Send the specified CPU's RCU callbacks to the orphanage. The
1894 * specified CPU must be offline, and the caller must hold the
1895 * ->orphan_lock.
1896 */
1897static void
1898rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
1899 struct rcu_node *rnp, struct rcu_data *rdp)
1900{
1901 /* No-CBs CPUs do not have orphanable callbacks. */
1902 if (rcu_is_nocb_cpu(rdp->cpu))
1903 return;
1904
1905 /*
1906 * Orphan the callbacks. First adjust the counts. This is safe
1907 * because _rcu_barrier() excludes CPU-hotplug operations, so it
1908 * cannot be running now. Thus no memory barrier is required.
1909 */
1910 if (rdp->nxtlist != NULL) {
1911 rsp->qlen_lazy += rdp->qlen_lazy;
1912 rsp->qlen += rdp->qlen;
1913 rdp->n_cbs_orphaned += rdp->qlen;
1914 rdp->qlen_lazy = 0;
1915 ACCESS_ONCE(rdp->qlen) = 0;
1916 }
1917
1918 /*
1919 * Next, move those callbacks still needing a grace period to
1920 * the orphanage, where some other CPU will pick them up.
1921 * Some of the callbacks might have gone partway through a grace
1922 * period, but that is too bad. They get to start over because we
1923 * cannot assume that grace periods are synchronized across CPUs.
1924 * We don't bother updating the ->nxttail[] array yet, instead
1925 * we just reset the whole thing later on.
1926 */
1927 if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
1928 *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
1929 rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
1930 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1931 }
1932
1933 /*
1934 * Then move the ready-to-invoke callbacks to the orphanage,
1935 * where some other CPU will pick them up. These will not be
1936 * required to pass though another grace period: They are done.
1937 */
1938 if (rdp->nxtlist != NULL) {
1939 *rsp->orphan_donetail = rdp->nxtlist;
1940 rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
1941 }
1942
1943 /* Finally, initialize the rcu_data structure's list to empty. */
1944 init_callback_list(rdp);
1945}
1946
1947/*
1948 * Adopt the RCU callbacks from the specified rcu_state structure's
1949 * orphanage. The caller must hold the ->orphan_lock.
1950 */
1951static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
1952{
1953 int i;
1954 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
1955
1956 /* No-CBs CPUs are handled specially. */
1957 if (rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
1958 return;
1959
1960 /* Do the accounting first. */
1961 rdp->qlen_lazy += rsp->qlen_lazy;
1962 rdp->qlen += rsp->qlen;
1963 rdp->n_cbs_adopted += rsp->qlen;
1964 if (rsp->qlen_lazy != rsp->qlen)
1965 rcu_idle_count_callbacks_posted();
1966 rsp->qlen_lazy = 0;
1967 rsp->qlen = 0;
1968
1969 /*
1970 * We do not need a memory barrier here because the only way we
1971 * can get here if there is an rcu_barrier() in flight is if
1972 * we are the task doing the rcu_barrier().
1973 */
1974
1975 /* First adopt the ready-to-invoke callbacks. */
1976 if (rsp->orphan_donelist != NULL) {
1977 *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
1978 *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
1979 for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
1980 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
1981 rdp->nxttail[i] = rsp->orphan_donetail;
1982 rsp->orphan_donelist = NULL;
1983 rsp->orphan_donetail = &rsp->orphan_donelist;
1984 }
1985
1986 /* And then adopt the callbacks that still need a grace period. */
1987 if (rsp->orphan_nxtlist != NULL) {
1988 *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
1989 rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
1990 rsp->orphan_nxtlist = NULL;
1991 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
1992 }
1993}
1994
1995/*
1996 * Trace the fact that this CPU is going offline.
1997 */
1998static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
1999{
2000 RCU_TRACE(unsigned long mask);
2001 RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
2002 RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
2003
2004 RCU_TRACE(mask = rdp->grpmask);
2005 trace_rcu_grace_period(rsp->name,
2006 rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2007 TPS("cpuofl"));
2008}
2009
2010/*
2011 * The CPU has been completely removed, and some other CPU is reporting
2012 * this fact from process context. Do the remainder of the cleanup,
2013 * including orphaning the outgoing CPU's RCU callbacks, and also
2014 * adopting them. There can only be one CPU hotplug operation at a time,
2015 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2016 */
2017static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2018{
2019 unsigned long flags;
2020 unsigned long mask;
2021 int need_report = 0;
2022 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2023 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2024
2025 /* Adjust any no-longer-needed kthreads. */
2026 rcu_boost_kthread_setaffinity(rnp, -1);
2027
2028 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
2029
2030 /* Exclude any attempts to start a new grace period. */
2031 mutex_lock(&rsp->onoff_mutex);
2032 raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2033
2034 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2035 rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2036 rcu_adopt_orphan_cbs(rsp, flags);
2037
2038 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
2039 mask = rdp->grpmask; /* rnp->grplo is constant. */
2040 do {
2041 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
2042 smp_mb__after_unlock_lock();
2043 rnp->qsmaskinit &= ~mask;
2044 if (rnp->qsmaskinit != 0) {
2045 if (rnp != rdp->mynode)
2046 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
2047 break;
2048 }
2049 if (rnp == rdp->mynode)
2050 need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
2051 else
2052 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
2053 mask = rnp->grpmask;
2054 rnp = rnp->parent;
2055 } while (rnp != NULL);
2056
2057 /*
2058 * We still hold the leaf rcu_node structure lock here, and
2059 * irqs are still disabled. The reason for this subterfuge is
2060 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
2061 * held leads to deadlock.
2062 */
2063 raw_spin_unlock(&rsp->orphan_lock); /* irqs remain disabled. */
2064 rnp = rdp->mynode;
2065 if (need_report & RCU_OFL_TASKS_NORM_GP)
2066 rcu_report_unblock_qs_rnp(rnp, flags);
2067 else
2068 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2069 if (need_report & RCU_OFL_TASKS_EXP_GP)
2070 rcu_report_exp_rnp(rsp, rnp, true);
2071 WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
2072 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2073 cpu, rdp->qlen, rdp->nxtlist);
2074 init_callback_list(rdp);
2075 /* Disallow further callbacks on this CPU. */
2076 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2077 mutex_unlock(&rsp->onoff_mutex);
2078}
2079
2080#else /* #ifdef CONFIG_HOTPLUG_CPU */
2081
2082static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2083{
2084}
2085
2086static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2087{
2088}
2089
2090#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
2091
2092/*
2093 * Invoke any RCU callbacks that have made it to the end of their grace
2094 * period. Thottle as specified by rdp->blimit.
2095 */
2096static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2097{
2098 unsigned long flags;
2099 struct rcu_head *next, *list, **tail;
2100 long bl, count, count_lazy;
2101 int i;
2102
2103 /* If no callbacks are ready, just return. */
2104 if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2105 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2106 trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
2107 need_resched(), is_idle_task(current),
2108 rcu_is_callbacks_kthread());
2109 return;
2110 }
2111
2112 /*
2113 * Extract the list of ready callbacks, disabling to prevent
2114 * races with call_rcu() from interrupt handlers.
2115 */
2116 local_irq_save(flags);
2117 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2118 bl = rdp->blimit;
2119 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2120 list = rdp->nxtlist;
2121 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
2122 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2123 tail = rdp->nxttail[RCU_DONE_TAIL];
2124 for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
2125 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2126 rdp->nxttail[i] = &rdp->nxtlist;
2127 local_irq_restore(flags);
2128
2129 /* Invoke callbacks. */
2130 count = count_lazy = 0;
2131 while (list) {
2132 next = list->next;
2133 prefetch(next);
2134 debug_rcu_head_unqueue(list);
2135 if (__rcu_reclaim(rsp->name, list))
2136 count_lazy++;
2137 list = next;
2138 /* Stop only if limit reached and CPU has something to do. */
2139 if (++count >= bl &&
2140 (need_resched() ||
2141 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2142 break;
2143 }
2144
2145 local_irq_save(flags);
2146 trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
2147 is_idle_task(current),
2148 rcu_is_callbacks_kthread());
2149
2150 /* Update count, and requeue any remaining callbacks. */
2151 if (list != NULL) {
2152 *tail = rdp->nxtlist;
2153 rdp->nxtlist = list;
2154 for (i = 0; i < RCU_NEXT_SIZE; i++)
2155 if (&rdp->nxtlist == rdp->nxttail[i])
2156 rdp->nxttail[i] = tail;
2157 else
2158 break;
2159 }
2160 smp_mb(); /* List handling before counting for rcu_barrier(). */
2161 rdp->qlen_lazy -= count_lazy;
2162 ACCESS_ONCE(rdp->qlen) -= count;
2163 rdp->n_cbs_invoked += count;
2164
2165 /* Reinstate batch limit if we have worked down the excess. */
2166 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
2167 rdp->blimit = blimit;
2168
2169 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2170 if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
2171 rdp->qlen_last_fqs_check = 0;
2172 rdp->n_force_qs_snap = rsp->n_force_qs;
2173 } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
2174 rdp->qlen_last_fqs_check = rdp->qlen;
2175 WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2176
2177 local_irq_restore(flags);
2178
2179 /* Re-invoke RCU core processing if there are callbacks remaining. */
2180 if (cpu_has_callbacks_ready_to_invoke(rdp))
2181 invoke_rcu_core();
2182}
2183
2184/*
2185 * Check to see if this CPU is in a non-context-switch quiescent state
2186 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2187 * Also schedule RCU core processing.
2188 *
2189 * This function must be called from hardirq context. It is normally
2190 * invoked from the scheduling-clock interrupt. If rcu_pending returns
2191 * false, there is no point in invoking rcu_check_callbacks().
2192 */
2193void rcu_check_callbacks(int cpu, int user)
2194{
2195 trace_rcu_utilization(TPS("Start scheduler-tick"));
2196 increment_cpu_stall_ticks();
2197 if (user || rcu_is_cpu_rrupt_from_idle()) {
2198
2199 /*
2200 * Get here if this CPU took its interrupt from user
2201 * mode or from the idle loop, and if this is not a
2202 * nested interrupt. In this case, the CPU is in
2203 * a quiescent state, so note it.
2204 *
2205 * No memory barrier is required here because both
2206 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2207 * variables that other CPUs neither access nor modify,
2208 * at least not while the corresponding CPU is online.
2209 */
2210
2211 rcu_sched_qs(cpu);
2212 rcu_bh_qs(cpu);
2213
2214 } else if (!in_softirq()) {
2215
2216 /*
2217 * Get here if this CPU did not take its interrupt from
2218 * softirq, in other words, if it is not interrupting
2219 * a rcu_bh read-side critical section. This is an _bh
2220 * critical section, so note it.
2221 */
2222
2223 rcu_bh_qs(cpu);
2224 }
2225 rcu_preempt_check_callbacks(cpu);
2226 if (rcu_pending(cpu))
2227 invoke_rcu_core();
2228 trace_rcu_utilization(TPS("End scheduler-tick"));
2229}
2230
2231/*
2232 * Scan the leaf rcu_node structures, processing dyntick state for any that
2233 * have not yet encountered a quiescent state, using the function specified.
2234 * Also initiate boosting for any threads blocked on the root rcu_node.
2235 *
2236 * The caller must have suppressed start of new grace periods.
2237 */
2238static void force_qs_rnp(struct rcu_state *rsp,
2239 int (*f)(struct rcu_data *rsp, bool *isidle,
2240 unsigned long *maxj),
2241 bool *isidle, unsigned long *maxj)
2242{
2243 unsigned long bit;
2244 int cpu;
2245 unsigned long flags;
2246 unsigned long mask;
2247 struct rcu_node *rnp;
2248
2249 rcu_for_each_leaf_node(rsp, rnp) {
2250 cond_resched();
2251 mask = 0;
2252 raw_spin_lock_irqsave(&rnp->lock, flags);
2253 smp_mb__after_unlock_lock();
2254 if (!rcu_gp_in_progress(rsp)) {
2255 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2256 return;
2257 }
2258 if (rnp->qsmask == 0) {
2259 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
2260 continue;
2261 }
2262 cpu = rnp->grplo;
2263 bit = 1;
2264 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2265 if ((rnp->qsmask & bit) != 0) {
2266 if ((rnp->qsmaskinit & bit) != 0)
2267 *isidle = 0;
2268 if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
2269 mask |= bit;
2270 }
2271 }
2272 if (mask != 0) {
2273
2274 /* rcu_report_qs_rnp() releases rnp->lock. */
2275 rcu_report_qs_rnp(mask, rsp, rnp, flags);
2276 continue;
2277 }
2278 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2279 }
2280 rnp = rcu_get_root(rsp);
2281 if (rnp->qsmask == 0) {
2282 raw_spin_lock_irqsave(&rnp->lock, flags);
2283 smp_mb__after_unlock_lock();
2284 rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
2285 }
2286}
2287
2288/*
2289 * Force quiescent states on reluctant CPUs, and also detect which
2290 * CPUs are in dyntick-idle mode.
2291 */
2292static void force_quiescent_state(struct rcu_state *rsp)
2293{
2294 unsigned long flags;
2295 bool ret;
2296 struct rcu_node *rnp;
2297 struct rcu_node *rnp_old = NULL;
2298
2299 /* Funnel through hierarchy to reduce memory contention. */
2300 rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
2301 for (; rnp != NULL; rnp = rnp->parent) {
2302 ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2303 !raw_spin_trylock(&rnp->fqslock);
2304 if (rnp_old != NULL)
2305 raw_spin_unlock(&rnp_old->fqslock);
2306 if (ret) {
2307 ACCESS_ONCE(rsp->n_force_qs_lh)++;
2308 return;
2309 }
2310 rnp_old = rnp;
2311 }
2312 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2313
2314 /* Reached the root of the rcu_node tree, acquire lock. */
2315 raw_spin_lock_irqsave(&rnp_old->lock, flags);
2316 smp_mb__after_unlock_lock();
2317 raw_spin_unlock(&rnp_old->fqslock);
2318 if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2319 ACCESS_ONCE(rsp->n_force_qs_lh)++;
2320 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2321 return; /* Someone beat us to it. */
2322 }
2323 rsp->gp_flags |= RCU_GP_FLAG_FQS;
2324 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2325 wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
2326}
2327
2328/*
2329 * This does the RCU core processing work for the specified rcu_state
2330 * and rcu_data structures. This may be called only from the CPU to
2331 * whom the rdp belongs.
2332 */
2333static void
2334__rcu_process_callbacks(struct rcu_state *rsp)
2335{
2336 unsigned long flags;
2337 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
2338
2339 WARN_ON_ONCE(rdp->beenonline == 0);
2340
2341 /* Update RCU state based on any recent quiescent states. */
2342 rcu_check_quiescent_state(rsp, rdp);
2343
2344 /* Does this CPU require a not-yet-started grace period? */
2345 local_irq_save(flags);
2346 if (cpu_needs_another_gp(rsp, rdp)) {
2347 raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
2348 rcu_start_gp(rsp);
2349 raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2350 } else {
2351 local_irq_restore(flags);
2352 }
2353
2354 /* If there are callbacks ready, invoke them. */
2355 if (cpu_has_callbacks_ready_to_invoke(rdp))
2356 invoke_rcu_callbacks(rsp, rdp);
2357
2358 /* Do any needed deferred wakeups of rcuo kthreads. */
2359 do_nocb_deferred_wakeup(rdp);
2360}
2361
2362/*
2363 * Do RCU core processing for the current CPU.
2364 */
2365static void rcu_process_callbacks(struct softirq_action *unused)
2366{
2367 struct rcu_state *rsp;
2368
2369 if (cpu_is_offline(smp_processor_id()))
2370 return;
2371 trace_rcu_utilization(TPS("Start RCU core"));
2372 for_each_rcu_flavor(rsp)
2373 __rcu_process_callbacks(rsp);
2374 trace_rcu_utilization(TPS("End RCU core"));
2375}
2376
2377/*
2378 * Schedule RCU callback invocation. If the specified type of RCU
2379 * does not support RCU priority boosting, just do a direct call,
2380 * otherwise wake up the per-CPU kernel kthread. Note that because we
2381 * are running on the current CPU with interrupts disabled, the
2382 * rcu_cpu_kthread_task cannot disappear out from under us.
2383 */
2384static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2385{
2386 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
2387 return;
2388 if (likely(!rsp->boost)) {
2389 rcu_do_batch(rsp, rdp);
2390 return;
2391 }
2392 invoke_rcu_callbacks_kthread();
2393}
2394
2395static void invoke_rcu_core(void)
2396{
2397 if (cpu_online(smp_processor_id()))
2398 raise_softirq(RCU_SOFTIRQ);
2399}
2400
2401/*
2402 * Handle any core-RCU processing required by a call_rcu() invocation.
2403 */
2404static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
2405 struct rcu_head *head, unsigned long flags)
2406{
2407 /*
2408 * If called from an extended quiescent state, invoke the RCU
2409 * core in order to force a re-evaluation of RCU's idleness.
2410 */
2411 if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2412 invoke_rcu_core();
2413
2414 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2415 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2416 return;
2417
2418 /*
2419 * Force the grace period if too many callbacks or too long waiting.
2420 * Enforce hysteresis, and don't invoke force_quiescent_state()
2421 * if some other CPU has recently done so. Also, don't bother
2422 * invoking force_quiescent_state() if the newly enqueued callback
2423 * is the only one waiting for a grace period to complete.
2424 */
2425 if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2426
2427 /* Are we ignoring a completed grace period? */
2428 note_gp_changes(rsp, rdp);
2429
2430 /* Start a new grace period if one not already started. */
2431 if (!rcu_gp_in_progress(rsp)) {
2432 struct rcu_node *rnp_root = rcu_get_root(rsp);
2433
2434 raw_spin_lock(&rnp_root->lock);
2435 smp_mb__after_unlock_lock();
2436 rcu_start_gp(rsp);
2437 raw_spin_unlock(&rnp_root->lock);
2438 } else {
2439 /* Give the grace period a kick. */
2440 rdp->blimit = LONG_MAX;
2441 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
2442 *rdp->nxttail[RCU_DONE_TAIL] != head)
2443 force_quiescent_state(rsp);
2444 rdp->n_force_qs_snap = rsp->n_force_qs;
2445 rdp->qlen_last_fqs_check = rdp->qlen;
2446 }
2447 }
2448}
2449
2450/*
2451 * RCU callback function to leak a callback.
2452 */
2453static void rcu_leak_callback(struct rcu_head *rhp)
2454{
2455}
2456
2457/*
2458 * Helper function for call_rcu() and friends. The cpu argument will
2459 * normally be -1, indicating "currently running CPU". It may specify
2460 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
2461 * is expected to specify a CPU.
2462 */
2463static void
2464__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
2465 struct rcu_state *rsp, int cpu, bool lazy)
2466{
2467 unsigned long flags;
2468 struct rcu_data *rdp;
2469
2470 WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
2471 if (debug_rcu_head_queue(head)) {
2472 /* Probable double call_rcu(), so leak the callback. */
2473 ACCESS_ONCE(head->func) = rcu_leak_callback;
2474 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
2475 return;
2476 }
2477 head->func = func;
2478 head->next = NULL;
2479
2480 /*
2481 * Opportunistically note grace-period endings and beginnings.
2482 * Note that we might see a beginning right after we see an
2483 * end, but never vice versa, since this CPU has to pass through
2484 * a quiescent state betweentimes.
2485 */
2486 local_irq_save(flags);
2487 rdp = this_cpu_ptr(rsp->rda);
2488
2489 /* Add the callback to our list. */
2490 if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
2491 int offline;
2492
2493 if (cpu != -1)
2494 rdp = per_cpu_ptr(rsp->rda, cpu);
2495 offline = !__call_rcu_nocb(rdp, head, lazy, flags);
2496 WARN_ON_ONCE(offline);
2497 /* _call_rcu() is illegal on offline CPU; leak the callback. */
2498 local_irq_restore(flags);
2499 return;
2500 }
2501 ACCESS_ONCE(rdp->qlen)++;
2502 if (lazy)
2503 rdp->qlen_lazy++;
2504 else
2505 rcu_idle_count_callbacks_posted();
2506 smp_mb(); /* Count before adding callback for rcu_barrier(). */
2507 *rdp->nxttail[RCU_NEXT_TAIL] = head;
2508 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
2509
2510 if (__is_kfree_rcu_offset((unsigned long)func))
2511 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
2512 rdp->qlen_lazy, rdp->qlen);
2513 else
2514 trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
2515
2516 /* Go handle any RCU core processing required. */
2517 __call_rcu_core(rsp, rdp, head, flags);
2518 local_irq_restore(flags);
2519}
2520
2521/*
2522 * Queue an RCU-sched callback for invocation after a grace period.
2523 */
2524void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2525{
2526 __call_rcu(head, func, &rcu_sched_state, -1, 0);
2527}
2528EXPORT_SYMBOL_GPL(call_rcu_sched);
2529
2530/*
2531 * Queue an RCU callback for invocation after a quicker grace period.
2532 */
2533void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2534{
2535 __call_rcu(head, func, &rcu_bh_state, -1, 0);
2536}
2537EXPORT_SYMBOL_GPL(call_rcu_bh);
2538
2539/*
2540 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2541 * any blocking grace-period wait automatically implies a grace period
2542 * if there is only one CPU online at any point time during execution
2543 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2544 * occasionally incorrectly indicate that there are multiple CPUs online
2545 * when there was in fact only one the whole time, as this just adds
2546 * some overhead: RCU still operates correctly.
2547 */
2548static inline int rcu_blocking_is_gp(void)
2549{
2550 int ret;
2551
2552 might_sleep(); /* Check for RCU read-side critical section. */
2553 preempt_disable();
2554 ret = num_online_cpus() <= 1;
2555 preempt_enable();
2556 return ret;
2557}
2558
2559/**
2560 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2561 *
2562 * Control will return to the caller some time after a full rcu-sched
2563 * grace period has elapsed, in other words after all currently executing
2564 * rcu-sched read-side critical sections have completed. These read-side
2565 * critical sections are delimited by rcu_read_lock_sched() and
2566 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2567 * local_irq_disable(), and so on may be used in place of
2568 * rcu_read_lock_sched().
2569 *
2570 * This means that all preempt_disable code sequences, including NMI and
2571 * non-threaded hardware-interrupt handlers, in progress on entry will
2572 * have completed before this primitive returns. However, this does not
2573 * guarantee that softirq handlers will have completed, since in some
2574 * kernels, these handlers can run in process context, and can block.
2575 *
2576 * Note that this guarantee implies further memory-ordering guarantees.
2577 * On systems with more than one CPU, when synchronize_sched() returns,
2578 * each CPU is guaranteed to have executed a full memory barrier since the
2579 * end of its last RCU-sched read-side critical section whose beginning
2580 * preceded the call to synchronize_sched(). In addition, each CPU having
2581 * an RCU read-side critical section that extends beyond the return from
2582 * synchronize_sched() is guaranteed to have executed a full memory barrier
2583 * after the beginning of synchronize_sched() and before the beginning of
2584 * that RCU read-side critical section. Note that these guarantees include
2585 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
2586 * that are executing in the kernel.
2587 *
2588 * Furthermore, if CPU A invoked synchronize_sched(), which returned
2589 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
2590 * to have executed a full memory barrier during the execution of
2591 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
2592 * again only if the system has more than one CPU).
2593 *
2594 * This primitive provides the guarantees made by the (now removed)
2595 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2596 * guarantees that rcu_read_lock() sections will have completed.
2597 * In "classic RCU", these two guarantees happen to be one and
2598 * the same, but can differ in realtime RCU implementations.
2599 */
2600void synchronize_sched(void)
2601{
2602 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
2603 !lock_is_held(&rcu_lock_map) &&
2604 !lock_is_held(&rcu_sched_lock_map),
2605 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2606 if (rcu_blocking_is_gp())
2607 return;
2608 if (rcu_expedited)
2609 synchronize_sched_expedited();
2610 else
2611 wait_rcu_gp(call_rcu_sched);
2612}
2613EXPORT_SYMBOL_GPL(synchronize_sched);
2614
2615/**
2616 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2617 *
2618 * Control will return to the caller some time after a full rcu_bh grace
2619 * period has elapsed, in other words after all currently executing rcu_bh
2620 * read-side critical sections have completed. RCU read-side critical
2621 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2622 * and may be nested.
2623 *
2624 * See the description of synchronize_sched() for more detailed information
2625 * on memory ordering guarantees.
2626 */
2627void synchronize_rcu_bh(void)
2628{
2629 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
2630 !lock_is_held(&rcu_lock_map) &&
2631 !lock_is_held(&rcu_sched_lock_map),
2632 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2633 if (rcu_blocking_is_gp())
2634 return;
2635 if (rcu_expedited)
2636 synchronize_rcu_bh_expedited();
2637 else
2638 wait_rcu_gp(call_rcu_bh);
2639}
2640EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
2641
2642/**
2643 * get_state_synchronize_rcu - Snapshot current RCU state
2644 *
2645 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
2646 * to determine whether or not a full grace period has elapsed in the
2647 * meantime.
2648 */
2649unsigned long get_state_synchronize_rcu(void)
2650{
2651 /*
2652 * Any prior manipulation of RCU-protected data must happen
2653 * before the load from ->gpnum.
2654 */
2655 smp_mb(); /* ^^^ */
2656
2657 /*
2658 * Make sure this load happens before the purportedly
2659 * time-consuming work between get_state_synchronize_rcu()
2660 * and cond_synchronize_rcu().
2661 */
2662 return smp_load_acquire(&rcu_state->gpnum);
2663}
2664EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
2665
2666/**
2667 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
2668 *
2669 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
2670 *
2671 * If a full RCU grace period has elapsed since the earlier call to
2672 * get_state_synchronize_rcu(), just return. Otherwise, invoke
2673 * synchronize_rcu() to wait for a full grace period.
2674 *
2675 * Yes, this function does not take counter wrap into account. But
2676 * counter wrap is harmless. If the counter wraps, we have waited for
2677 * more than 2 billion grace periods (and way more on a 64-bit system!),
2678 * so waiting for one additional grace period should be just fine.
2679 */
2680void cond_synchronize_rcu(unsigned long oldstate)
2681{
2682 unsigned long newstate;
2683
2684 /*
2685 * Ensure that this load happens before any RCU-destructive
2686 * actions the caller might carry out after we return.
2687 */
2688 newstate = smp_load_acquire(&rcu_state->completed);
2689 if (ULONG_CMP_GE(oldstate, newstate))
2690 synchronize_rcu();
2691}
2692EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
2693
2694static int synchronize_sched_expedited_cpu_stop(void *data)
2695{
2696 /*
2697 * There must be a full memory barrier on each affected CPU
2698 * between the time that try_stop_cpus() is called and the
2699 * time that it returns.
2700 *
2701 * In the current initial implementation of cpu_stop, the
2702 * above condition is already met when the control reaches
2703 * this point and the following smp_mb() is not strictly
2704 * necessary. Do smp_mb() anyway for documentation and
2705 * robustness against future implementation changes.
2706 */
2707 smp_mb(); /* See above comment block. */
2708 return 0;
2709}
2710
2711/**
2712 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2713 *
2714 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2715 * approach to force the grace period to end quickly. This consumes
2716 * significant time on all CPUs and is unfriendly to real-time workloads,
2717 * so is thus not recommended for any sort of common-case code. In fact,
2718 * if you are using synchronize_sched_expedited() in a loop, please
2719 * restructure your code to batch your updates, and then use a single
2720 * synchronize_sched() instead.
2721 *
2722 * Note that it is illegal to call this function while holding any lock
2723 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2724 * to call this function from a CPU-hotplug notifier. Failing to observe
2725 * these restriction will result in deadlock.
2726 *
2727 * This implementation can be thought of as an application of ticket
2728 * locking to RCU, with sync_sched_expedited_started and
2729 * sync_sched_expedited_done taking on the roles of the halves
2730 * of the ticket-lock word. Each task atomically increments
2731 * sync_sched_expedited_started upon entry, snapshotting the old value,
2732 * then attempts to stop all the CPUs. If this succeeds, then each
2733 * CPU will have executed a context switch, resulting in an RCU-sched
2734 * grace period. We are then done, so we use atomic_cmpxchg() to
2735 * update sync_sched_expedited_done to match our snapshot -- but
2736 * only if someone else has not already advanced past our snapshot.
2737 *
2738 * On the other hand, if try_stop_cpus() fails, we check the value
2739 * of sync_sched_expedited_done. If it has advanced past our
2740 * initial snapshot, then someone else must have forced a grace period
2741 * some time after we took our snapshot. In this case, our work is
2742 * done for us, and we can simply return. Otherwise, we try again,
2743 * but keep our initial snapshot for purposes of checking for someone
2744 * doing our work for us.
2745 *
2746 * If we fail too many times in a row, we fall back to synchronize_sched().
2747 */
2748void synchronize_sched_expedited(void)
2749{
2750 long firstsnap, s, snap;
2751 int trycount = 0;
2752 struct rcu_state *rsp = &rcu_sched_state;
2753
2754 /*
2755 * If we are in danger of counter wrap, just do synchronize_sched().
2756 * By allowing sync_sched_expedited_started to advance no more than
2757 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
2758 * that more than 3.5 billion CPUs would be required to force a
2759 * counter wrap on a 32-bit system. Quite a few more CPUs would of
2760 * course be required on a 64-bit system.
2761 */
2762 if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
2763 (ulong)atomic_long_read(&rsp->expedited_done) +
2764 ULONG_MAX / 8)) {
2765 synchronize_sched();
2766 atomic_long_inc(&rsp->expedited_wrap);
2767 return;
2768 }
2769
2770 /*
2771 * Take a ticket. Note that atomic_inc_return() implies a
2772 * full memory barrier.
2773 */
2774 snap = atomic_long_inc_return(&rsp->expedited_start);
2775 firstsnap = snap;
2776 get_online_cpus();
2777 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2778
2779 /*
2780 * Each pass through the following loop attempts to force a
2781 * context switch on each CPU.
2782 */
2783 while (try_stop_cpus(cpu_online_mask,
2784 synchronize_sched_expedited_cpu_stop,
2785 NULL) == -EAGAIN) {
2786 put_online_cpus();
2787 atomic_long_inc(&rsp->expedited_tryfail);
2788
2789 /* Check to see if someone else did our work for us. */
2790 s = atomic_long_read(&rsp->expedited_done);
2791 if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
2792 /* ensure test happens before caller kfree */
2793 smp_mb__before_atomic_inc(); /* ^^^ */
2794 atomic_long_inc(&rsp->expedited_workdone1);
2795 return;
2796 }
2797
2798 /* No joy, try again later. Or just synchronize_sched(). */
2799 if (trycount++ < 10) {
2800 udelay(trycount * num_online_cpus());
2801 } else {
2802 wait_rcu_gp(call_rcu_sched);
2803 atomic_long_inc(&rsp->expedited_normal);
2804 return;
2805 }
2806
2807 /* Recheck to see if someone else did our work for us. */
2808 s = atomic_long_read(&rsp->expedited_done);
2809 if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
2810 /* ensure test happens before caller kfree */
2811 smp_mb__before_atomic_inc(); /* ^^^ */
2812 atomic_long_inc(&rsp->expedited_workdone2);
2813 return;
2814 }
2815
2816 /*
2817 * Refetching sync_sched_expedited_started allows later
2818 * callers to piggyback on our grace period. We retry
2819 * after they started, so our grace period works for them,
2820 * and they started after our first try, so their grace
2821 * period works for us.
2822 */
2823 get_online_cpus();
2824 snap = atomic_long_read(&rsp->expedited_start);
2825 smp_mb(); /* ensure read is before try_stop_cpus(). */
2826 }
2827 atomic_long_inc(&rsp->expedited_stoppedcpus);
2828
2829 /*
2830 * Everyone up to our most recent fetch is covered by our grace
2831 * period. Update the counter, but only if our work is still
2832 * relevant -- which it won't be if someone who started later
2833 * than we did already did their update.
2834 */
2835 do {
2836 atomic_long_inc(&rsp->expedited_done_tries);
2837 s = atomic_long_read(&rsp->expedited_done);
2838 if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
2839 /* ensure test happens before caller kfree */
2840 smp_mb__before_atomic_inc(); /* ^^^ */
2841 atomic_long_inc(&rsp->expedited_done_lost);
2842 break;
2843 }
2844 } while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
2845 atomic_long_inc(&rsp->expedited_done_exit);
2846
2847 put_online_cpus();
2848}
2849EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
2850
2851/*
2852 * Check to see if there is any immediate RCU-related work to be done
2853 * by the current CPU, for the specified type of RCU, returning 1 if so.
2854 * The checks are in order of increasing expense: checks that can be
2855 * carried out against CPU-local state are performed first. However,
2856 * we must check for CPU stalls first, else we might not get a chance.
2857 */
2858static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
2859{
2860 struct rcu_node *rnp = rdp->mynode;
2861
2862 rdp->n_rcu_pending++;
2863
2864 /* Check for CPU stalls, if enabled. */
2865 check_cpu_stall(rsp, rdp);
2866
2867 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
2868 if (rcu_nohz_full_cpu(rsp))
2869 return 0;
2870
2871 /* Is the RCU core waiting for a quiescent state from this CPU? */
2872 if (rcu_scheduler_fully_active &&
2873 rdp->qs_pending && !rdp->passed_quiesce) {
2874 rdp->n_rp_qs_pending++;
2875 } else if (rdp->qs_pending && rdp->passed_quiesce) {
2876 rdp->n_rp_report_qs++;
2877 return 1;
2878 }
2879
2880 /* Does this CPU have callbacks ready to invoke? */
2881 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
2882 rdp->n_rp_cb_ready++;
2883 return 1;
2884 }
2885
2886 /* Has RCU gone idle with this CPU needing another grace period? */
2887 if (cpu_needs_another_gp(rsp, rdp)) {
2888 rdp->n_rp_cpu_needs_gp++;
2889 return 1;
2890 }
2891
2892 /* Has another RCU grace period completed? */
2893 if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
2894 rdp->n_rp_gp_completed++;
2895 return 1;
2896 }
2897
2898 /* Has a new RCU grace period started? */
2899 if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
2900 rdp->n_rp_gp_started++;
2901 return 1;
2902 }
2903
2904 /* Does this CPU need a deferred NOCB wakeup? */
2905 if (rcu_nocb_need_deferred_wakeup(rdp)) {
2906 rdp->n_rp_nocb_defer_wakeup++;
2907 return 1;
2908 }
2909
2910 /* nothing to do */
2911 rdp->n_rp_need_nothing++;
2912 return 0;
2913}
2914
2915/*
2916 * Check to see if there is any immediate RCU-related work to be done
2917 * by the current CPU, returning 1 if so. This function is part of the
2918 * RCU implementation; it is -not- an exported member of the RCU API.
2919 */
2920static int rcu_pending(int cpu)
2921{
2922 struct rcu_state *rsp;
2923
2924 for_each_rcu_flavor(rsp)
2925 if (__rcu_pending(rsp, per_cpu_ptr(rsp->rda, cpu)))
2926 return 1;
2927 return 0;
2928}
2929
2930/*
2931 * Return true if the specified CPU has any callback. If all_lazy is
2932 * non-NULL, store an indication of whether all callbacks are lazy.
2933 * (If there are no callbacks, all of them are deemed to be lazy.)
2934 */
2935static int __maybe_unused rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
2936{
2937 bool al = true;
2938 bool hc = false;
2939 struct rcu_data *rdp;
2940 struct rcu_state *rsp;
2941
2942 for_each_rcu_flavor(rsp) {
2943 rdp = per_cpu_ptr(rsp->rda, cpu);
2944 if (!rdp->nxtlist)
2945 continue;
2946 hc = true;
2947 if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
2948 al = false;
2949 break;
2950 }
2951 }
2952 if (all_lazy)
2953 *all_lazy = al;
2954 return hc;
2955}
2956
2957/*
2958 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2959 * the compiler is expected to optimize this away.
2960 */
2961static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
2962 int cpu, unsigned long done)
2963{
2964 trace_rcu_barrier(rsp->name, s, cpu,
2965 atomic_read(&rsp->barrier_cpu_count), done);
2966}
2967
2968/*
2969 * RCU callback function for _rcu_barrier(). If we are last, wake
2970 * up the task executing _rcu_barrier().
2971 */
2972static void rcu_barrier_callback(struct rcu_head *rhp)
2973{
2974 struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
2975 struct rcu_state *rsp = rdp->rsp;
2976
2977 if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
2978 _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
2979 complete(&rsp->barrier_completion);
2980 } else {
2981 _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
2982 }
2983}
2984
2985/*
2986 * Called with preemption disabled, and from cross-cpu IRQ context.
2987 */
2988static void rcu_barrier_func(void *type)
2989{
2990 struct rcu_state *rsp = type;
2991 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
2992
2993 _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
2994 atomic_inc(&rsp->barrier_cpu_count);
2995 rsp->call(&rdp->barrier_head, rcu_barrier_callback);
2996}
2997
2998/*
2999 * Orchestrate the specified type of RCU barrier, waiting for all
3000 * RCU callbacks of the specified type to complete.
3001 */
3002static void _rcu_barrier(struct rcu_state *rsp)
3003{
3004 int cpu;
3005 struct rcu_data *rdp;
3006 unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
3007 unsigned long snap_done;
3008
3009 _rcu_barrier_trace(rsp, "Begin", -1, snap);
3010
3011 /* Take mutex to serialize concurrent rcu_barrier() requests. */
3012 mutex_lock(&rsp->barrier_mutex);
3013
3014 /*
3015 * Ensure that all prior references, including to ->n_barrier_done,
3016 * are ordered before the _rcu_barrier() machinery.
3017 */
3018 smp_mb(); /* See above block comment. */
3019
3020 /*
3021 * Recheck ->n_barrier_done to see if others did our work for us.
3022 * This means checking ->n_barrier_done for an even-to-odd-to-even
3023 * transition. The "if" expression below therefore rounds the old
3024 * value up to the next even number and adds two before comparing.
3025 */
3026 snap_done = rsp->n_barrier_done;
3027 _rcu_barrier_trace(rsp, "Check", -1, snap_done);
3028
3029 /*
3030 * If the value in snap is odd, we needed to wait for the current
3031 * rcu_barrier() to complete, then wait for the next one, in other
3032 * words, we need the value of snap_done to be three larger than
3033 * the value of snap. On the other hand, if the value in snap is
3034 * even, we only had to wait for the next rcu_barrier() to complete,
3035 * in other words, we need the value of snap_done to be only two
3036 * greater than the value of snap. The "(snap + 3) & ~0x1" computes
3037 * this for us (thank you, Linus!).
3038 */
3039 if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
3040 _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
3041 smp_mb(); /* caller's subsequent code after above check. */
3042 mutex_unlock(&rsp->barrier_mutex);
3043 return;
3044 }
3045
3046 /*
3047 * Increment ->n_barrier_done to avoid duplicate work. Use
3048 * ACCESS_ONCE() to prevent the compiler from speculating
3049 * the increment to precede the early-exit check.
3050 */
3051 ACCESS_ONCE(rsp->n_barrier_done)++;
3052 WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
3053 _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
3054 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3055
3056 /*
3057 * Initialize the count to one rather than to zero in order to
3058 * avoid a too-soon return to zero in case of a short grace period
3059 * (or preemption of this task). Exclude CPU-hotplug operations
3060 * to ensure that no offline CPU has callbacks queued.
3061 */
3062 init_completion(&rsp->barrier_completion);
3063 atomic_set(&rsp->barrier_cpu_count, 1);
3064 get_online_cpus();
3065
3066 /*
3067 * Force each CPU with callbacks to register a new callback.
3068 * When that callback is invoked, we will know that all of the
3069 * corresponding CPU's preceding callbacks have been invoked.
3070 */
3071 for_each_possible_cpu(cpu) {
3072 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
3073 continue;
3074 rdp = per_cpu_ptr(rsp->rda, cpu);
3075 if (rcu_is_nocb_cpu(cpu)) {
3076 _rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
3077 rsp->n_barrier_done);
3078 atomic_inc(&rsp->barrier_cpu_count);
3079 __call_rcu(&rdp->barrier_head, rcu_barrier_callback,
3080 rsp, cpu, 0);
3081 } else if (ACCESS_ONCE(rdp->qlen)) {
3082 _rcu_barrier_trace(rsp, "OnlineQ", cpu,
3083 rsp->n_barrier_done);
3084 smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3085 } else {
3086 _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
3087 rsp->n_barrier_done);
3088 }
3089 }
3090 put_online_cpus();
3091
3092 /*
3093 * Now that we have an rcu_barrier_callback() callback on each
3094 * CPU, and thus each counted, remove the initial count.
3095 */
3096 if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3097 complete(&rsp->barrier_completion);
3098
3099 /* Increment ->n_barrier_done to prevent duplicate work. */
3100 smp_mb(); /* Keep increment after above mechanism. */
3101 ACCESS_ONCE(rsp->n_barrier_done)++;
3102 WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
3103 _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
3104 smp_mb(); /* Keep increment before caller's subsequent code. */
3105
3106 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3107 wait_for_completion(&rsp->barrier_completion);
3108
3109 /* Other rcu_barrier() invocations can now safely proceed. */
3110 mutex_unlock(&rsp->barrier_mutex);
3111}
3112
3113/**
3114 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3115 */
3116void rcu_barrier_bh(void)
3117{
3118 _rcu_barrier(&rcu_bh_state);
3119}
3120EXPORT_SYMBOL_GPL(rcu_barrier_bh);
3121
3122/**
3123 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3124 */
3125void rcu_barrier_sched(void)
3126{
3127 _rcu_barrier(&rcu_sched_state);
3128}
3129EXPORT_SYMBOL_GPL(rcu_barrier_sched);
3130
3131/*
3132 * Do boot-time initialization of a CPU's per-CPU RCU data.
3133 */
3134static void __init
3135rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3136{
3137 unsigned long flags;
3138 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3139 struct rcu_node *rnp = rcu_get_root(rsp);
3140
3141 /* Set up local state, ensuring consistent view of global state. */
3142 raw_spin_lock_irqsave(&rnp->lock, flags);
3143 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
3144 init_callback_list(rdp);
3145 rdp->qlen_lazy = 0;
3146 ACCESS_ONCE(rdp->qlen) = 0;
3147 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3148 WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3149 WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
3150 rdp->cpu = cpu;
3151 rdp->rsp = rsp;
3152 rcu_boot_init_nocb_percpu_data(rdp);
3153 raw_spin_unlock_irqrestore(&rnp->lock, flags);
3154}
3155
3156/*
3157 * Initialize a CPU's per-CPU RCU data. Note that only one online or
3158 * offline event can be happening at a given time. Note also that we
3159 * can accept some slop in the rsp->completed access due to the fact
3160 * that this CPU cannot possibly have any RCU callbacks in flight yet.
3161 */
3162static void
3163rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
3164{
3165 unsigned long flags;
3166 unsigned long mask;
3167 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3168 struct rcu_node *rnp = rcu_get_root(rsp);
3169
3170 /* Exclude new grace periods. */
3171 mutex_lock(&rsp->onoff_mutex);
3172
3173 /* Set up local state, ensuring consistent view of global state. */
3174 raw_spin_lock_irqsave(&rnp->lock, flags);
3175 rdp->beenonline = 1; /* We have now been online. */
3176 rdp->preemptible = preemptible;
3177 rdp->qlen_last_fqs_check = 0;
3178 rdp->n_force_qs_snap = rsp->n_force_qs;
3179 rdp->blimit = blimit;
3180 init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
3181 rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3182 rcu_sysidle_init_percpu_data(rdp->dynticks);
3183 atomic_set(&rdp->dynticks->dynticks,
3184 (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
3185 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
3186
3187 /* Add CPU to rcu_node bitmasks. */
3188 rnp = rdp->mynode;
3189 mask = rdp->grpmask;
3190 do {
3191 /* Exclude any attempts to start a new GP on small systems. */
3192 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
3193 rnp->qsmaskinit |= mask;
3194 mask = rnp->grpmask;
3195 if (rnp == rdp->mynode) {
3196 /*
3197 * If there is a grace period in progress, we will
3198 * set up to wait for it next time we run the
3199 * RCU core code.
3200 */
3201 rdp->gpnum = rnp->completed;
3202 rdp->completed = rnp->completed;
3203 rdp->passed_quiesce = 0;
3204 rdp->qs_pending = 0;
3205 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3206 }
3207 raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
3208 rnp = rnp->parent;
3209 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
3210 local_irq_restore(flags);
3211
3212 mutex_unlock(&rsp->onoff_mutex);
3213}
3214
3215static void rcu_prepare_cpu(int cpu)
3216{
3217 struct rcu_state *rsp;
3218
3219 for_each_rcu_flavor(rsp)
3220 rcu_init_percpu_data(cpu, rsp,
3221 strcmp(rsp->name, "rcu_preempt") == 0);
3222}
3223
3224/*
3225 * Handle CPU online/offline notification events.
3226 */
3227static int rcu_cpu_notify(struct notifier_block *self,
3228 unsigned long action, void *hcpu)
3229{
3230 long cpu = (long)hcpu;
3231 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
3232 struct rcu_node *rnp = rdp->mynode;
3233 struct rcu_state *rsp;
3234
3235 trace_rcu_utilization(TPS("Start CPU hotplug"));
3236 switch (action) {
3237 case CPU_UP_PREPARE:
3238 case CPU_UP_PREPARE_FROZEN:
3239 rcu_prepare_cpu(cpu);
3240 rcu_prepare_kthreads(cpu);
3241 break;
3242 case CPU_ONLINE:
3243 case CPU_DOWN_FAILED:
3244 rcu_boost_kthread_setaffinity(rnp, -1);
3245 break;
3246 case CPU_DOWN_PREPARE:
3247 rcu_boost_kthread_setaffinity(rnp, cpu);
3248 break;
3249 case CPU_DYING:
3250 case CPU_DYING_FROZEN:
3251 for_each_rcu_flavor(rsp)
3252 rcu_cleanup_dying_cpu(rsp);
3253 break;
3254 case CPU_DEAD:
3255 case CPU_DEAD_FROZEN:
3256 case CPU_UP_CANCELED:
3257 case CPU_UP_CANCELED_FROZEN:
3258 for_each_rcu_flavor(rsp)
3259 rcu_cleanup_dead_cpu(cpu, rsp);
3260 break;
3261 default:
3262 break;
3263 }
3264 trace_rcu_utilization(TPS("End CPU hotplug"));
3265 return NOTIFY_OK;
3266}
3267
3268static int rcu_pm_notify(struct notifier_block *self,
3269 unsigned long action, void *hcpu)
3270{
3271 switch (action) {
3272 case PM_HIBERNATION_PREPARE:
3273 case PM_SUSPEND_PREPARE:
3274 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3275 rcu_expedited = 1;
3276 break;
3277 case PM_POST_HIBERNATION:
3278 case PM_POST_SUSPEND:
3279 rcu_expedited = 0;
3280 break;
3281 default:
3282 break;
3283 }
3284 return NOTIFY_OK;
3285}
3286
3287/*
3288 * Spawn the kthread that handles this RCU flavor's grace periods.
3289 */
3290static int __init rcu_spawn_gp_kthread(void)
3291{
3292 unsigned long flags;
3293 struct rcu_node *rnp;
3294 struct rcu_state *rsp;
3295 struct task_struct *t;
3296
3297 for_each_rcu_flavor(rsp) {
3298 t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
3299 BUG_ON(IS_ERR(t));
3300 rnp = rcu_get_root(rsp);
3301 raw_spin_lock_irqsave(&rnp->lock, flags);
3302 rsp->gp_kthread = t;
3303 raw_spin_unlock_irqrestore(&rnp->lock, flags);
3304 rcu_spawn_nocb_kthreads(rsp);
3305 }
3306 return 0;
3307}
3308early_initcall(rcu_spawn_gp_kthread);
3309
3310/*
3311 * This function is invoked towards the end of the scheduler's initialization
3312 * process. Before this is called, the idle task might contain
3313 * RCU read-side critical sections (during which time, this idle
3314 * task is booting the system). After this function is called, the
3315 * idle tasks are prohibited from containing RCU read-side critical
3316 * sections. This function also enables RCU lockdep checking.
3317 */
3318void rcu_scheduler_starting(void)
3319{
3320 WARN_ON(num_online_cpus() != 1);
3321 WARN_ON(nr_context_switches() > 0);
3322 rcu_scheduler_active = 1;
3323}
3324
3325/*
3326 * Compute the per-level fanout, either using the exact fanout specified
3327 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
3328 */
3329#ifdef CONFIG_RCU_FANOUT_EXACT
3330static void __init rcu_init_levelspread(struct rcu_state *rsp)
3331{
3332 int i;
3333
3334 rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
3335 for (i = rcu_num_lvls - 2; i >= 0; i--)
3336 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
3337}
3338#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
3339static void __init rcu_init_levelspread(struct rcu_state *rsp)
3340{
3341 int ccur;
3342 int cprv;
3343 int i;
3344
3345 cprv = nr_cpu_ids;
3346 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3347 ccur = rsp->levelcnt[i];
3348 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
3349 cprv = ccur;
3350 }
3351}
3352#endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
3353
3354/*
3355 * Helper function for rcu_init() that initializes one rcu_state structure.
3356 */
3357static void __init rcu_init_one(struct rcu_state *rsp,
3358 struct rcu_data __percpu *rda)
3359{
3360 static char *buf[] = { "rcu_node_0",
3361 "rcu_node_1",
3362 "rcu_node_2",
3363 "rcu_node_3" }; /* Match MAX_RCU_LVLS */
3364 static char *fqs[] = { "rcu_node_fqs_0",
3365 "rcu_node_fqs_1",
3366 "rcu_node_fqs_2",
3367 "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */
3368 int cpustride = 1;
3369 int i;
3370 int j;
3371 struct rcu_node *rnp;
3372
3373 BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
3374
3375 /* Silence gcc 4.8 warning about array index out of range. */
3376 if (rcu_num_lvls > RCU_NUM_LVLS)
3377 panic("rcu_init_one: rcu_num_lvls overflow");
3378
3379 /* Initialize the level-tracking arrays. */
3380
3381 for (i = 0; i < rcu_num_lvls; i++)
3382 rsp->levelcnt[i] = num_rcu_lvl[i];
3383 for (i = 1; i < rcu_num_lvls; i++)
3384 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
3385 rcu_init_levelspread(rsp);
3386
3387 /* Initialize the elements themselves, starting from the leaves. */
3388
3389 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3390 cpustride *= rsp->levelspread[i];
3391 rnp = rsp->level[i];
3392 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
3393 raw_spin_lock_init(&rnp->lock);
3394 lockdep_set_class_and_name(&rnp->lock,
3395 &rcu_node_class[i], buf[i]);
3396 raw_spin_lock_init(&rnp->fqslock);
3397 lockdep_set_class_and_name(&rnp->fqslock,
3398 &rcu_fqs_class[i], fqs[i]);
3399 rnp->gpnum = rsp->gpnum;
3400 rnp->completed = rsp->completed;
3401 rnp->qsmask = 0;
3402 rnp->qsmaskinit = 0;
3403 rnp->grplo = j * cpustride;
3404 rnp->grphi = (j + 1) * cpustride - 1;
3405 if (rnp->grphi >= NR_CPUS)
3406 rnp->grphi = NR_CPUS - 1;
3407 if (i == 0) {
3408 rnp->grpnum = 0;
3409 rnp->grpmask = 0;
3410 rnp->parent = NULL;
3411 } else {
3412 rnp->grpnum = j % rsp->levelspread[i - 1];
3413 rnp->grpmask = 1UL << rnp->grpnum;
3414 rnp->parent = rsp->level[i - 1] +
3415 j / rsp->levelspread[i - 1];
3416 }
3417 rnp->level = i;
3418 INIT_LIST_HEAD(&rnp->blkd_tasks);
3419 rcu_init_one_nocb(rnp);
3420 }
3421 }
3422
3423 rsp->rda = rda;
3424 init_waitqueue_head(&rsp->gp_wq);
3425 init_irq_work(&rsp->wakeup_work, rsp_wakeup);
3426 rnp = rsp->level[rcu_num_lvls - 1];
3427 for_each_possible_cpu(i) {
3428 while (i > rnp->grphi)
3429 rnp++;
3430 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
3431 rcu_boot_init_percpu_data(i, rsp);
3432 }
3433 list_add(&rsp->flavors, &rcu_struct_flavors);
3434}
3435
3436/*
3437 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3438 * replace the definitions in tree.h because those are needed to size
3439 * the ->node array in the rcu_state structure.
3440 */
3441static void __init rcu_init_geometry(void)
3442{
3443 ulong d;
3444 int i;
3445 int j;
3446 int n = nr_cpu_ids;
3447 int rcu_capacity[MAX_RCU_LVLS + 1];
3448
3449 /*
3450 * Initialize any unspecified boot parameters.
3451 * The default values of jiffies_till_first_fqs and
3452 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3453 * value, which is a function of HZ, then adding one for each
3454 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3455 */
3456 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
3457 if (jiffies_till_first_fqs == ULONG_MAX)
3458 jiffies_till_first_fqs = d;
3459 if (jiffies_till_next_fqs == ULONG_MAX)
3460 jiffies_till_next_fqs = d;
3461
3462 /* If the compile-time values are accurate, just leave. */
3463 if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
3464 nr_cpu_ids == NR_CPUS)
3465 return;
3466 pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
3467 rcu_fanout_leaf, nr_cpu_ids);
3468
3469 /*
3470 * Compute number of nodes that can be handled an rcu_node tree
3471 * with the given number of levels. Setting rcu_capacity[0] makes
3472 * some of the arithmetic easier.
3473 */
3474 rcu_capacity[0] = 1;
3475 rcu_capacity[1] = rcu_fanout_leaf;
3476 for (i = 2; i <= MAX_RCU_LVLS; i++)
3477 rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;
3478
3479 /*
3480 * The boot-time rcu_fanout_leaf parameter is only permitted
3481 * to increase the leaf-level fanout, not decrease it. Of course,
3482 * the leaf-level fanout cannot exceed the number of bits in
3483 * the rcu_node masks. Finally, the tree must be able to accommodate
3484 * the configured number of CPUs. Complain and fall back to the
3485 * compile-time values if these limits are exceeded.
3486 */
3487 if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
3488 rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
3489 n > rcu_capacity[MAX_RCU_LVLS]) {
3490 WARN_ON(1);
3491 return;
3492 }
3493
3494 /* Calculate the number of rcu_nodes at each level of the tree. */
3495 for (i = 1; i <= MAX_RCU_LVLS; i++)
3496 if (n <= rcu_capacity[i]) {
3497 for (j = 0; j <= i; j++)
3498 num_rcu_lvl[j] =
3499 DIV_ROUND_UP(n, rcu_capacity[i - j]);
3500 rcu_num_lvls = i;
3501 for (j = i + 1; j <= MAX_RCU_LVLS; j++)
3502 num_rcu_lvl[j] = 0;
3503 break;
3504 }
3505
3506 /* Calculate the total number of rcu_node structures. */
3507 rcu_num_nodes = 0;
3508 for (i = 0; i <= MAX_RCU_LVLS; i++)
3509 rcu_num_nodes += num_rcu_lvl[i];
3510 rcu_num_nodes -= n;
3511}
3512
3513void __init rcu_init(void)
3514{
3515 int cpu;
3516
3517 rcu_bootup_announce();
3518 rcu_init_geometry();
3519 rcu_init_one(&rcu_bh_state, &rcu_bh_data);
3520 rcu_init_one(&rcu_sched_state, &rcu_sched_data);
3521 __rcu_init_preempt();
3522 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
3523
3524 /*
3525 * We don't need protection against CPU-hotplug here because
3526 * this is called early in boot, before either interrupts
3527 * or the scheduler are operational.
3528 */
3529 cpu_notifier(rcu_cpu_notify, 0);
3530 pm_notifier(rcu_pm_notify, 0);
3531 for_each_online_cpu(cpu)
3532 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
3533}
3534
3535#include "tree_plugin.h"